Subthreshold defect formation in YBa 2Cu 3 O7-δ at nonuniform heating of electron gas in electromagnetic field
In YBa2Cu3O7-δ high temperature superconductors with δ<0.3 the irradiation by super high-frequency electromagnetic field with impulse power 104-106 W gives rise to a decrease of the rates of annihilation and capture of positrons, a growth of resistance, residual resistance, thermopower an...
Gespeichert in:
| Datum: | 2002 |
|---|---|
| Hauptverfasser: | , , , , , |
| Format: | Artikel |
| Sprache: | Englisch |
| Veröffentlicht: |
Chuiko Institute of Surface Chemistry National Academy of Sciences of Ukraine
2002
|
| Online Zugang: | https://surfacezbir.com.ua/index.php/surface/article/view/84 |
| Tags: |
Tag hinzufügen
Keine Tags, Fügen Sie den ersten Tag hinzu!
|
| Назва журналу: | Surface |
| Завантажити файл: |  |
Institution
Surface| _version_ | 1869291172709531648 |
|---|---|
| author | Adokin, V. T. Gorelov, B. M. Ogenko, V. M. Melnikov, V. S. Kevdina, I. B. Shalyapina, G. M. |
| author_facet | Adokin, V. T. Gorelov, B. M. Ogenko, V. M. Melnikov, V. S. Kevdina, I. B. Shalyapina, G. M. |
| author_institution_txt_mv | [
{
"author": "V. T. Adokin",
"institution": "Інститут хімії поверхні НАН України"
},
{
"author": "B. M. Gorelov",
"institution": "Інститут хімії поверхні НАН України"
},
{
"author": "V. M. Ogenko",
"institution": "Інститут хімії поверхні НАН України"
},
{
"author": "V. S. Melnikov",
"institution": "Institute of Geochemistry, Mineralogy and Oreformation"
},
{
"author": "I. B. Kevdina",
"institution": "Institute of Chemical Physics"
},
{
"author": "G. M. Shalyapina",
"institution": "Research Institute of Applied Physics"
}
] |
| author_sort | Adokin, V. T. |
| baseUrl_str | |
| collection | OJS |
| datestamp_date | 2018-11-27T09:42:19Z |
| description | In YBa2Cu3O7-δ high temperature superconductors with δ<0.3 the irradiation by super high-frequency electromagnetic field with impulse power 104-106 W gives rise to a decrease of the rates of annihilation and capture of positrons, a growth of resistance, residual resistance, thermopower and the block of diffusive transitions of Au atoms, which are caused by the subthreshold defect formation in the intermediate layers. The irradiation effect is enhanced with rise of the number of defects in samples and does not depend on an impulse power. The defect formation is related to the excitation of low-frequency weakly damped collective excitations under irradiation, whose propagation through the crystal is accompanied by the Coulomb ejection of atoms from the lattice sites and the transformation and transport of defects. |
| first_indexed | 2025-07-22T19:30:09Z |
| format | Article |
| fulltext |
69
SUBTHRESHOLD DEFECT FORMATION IN YBa 2Cu 3 O7-δ
AT NONUNIFORM HEATING OF ELECTRON GAS
IN ELECTROMAGNETIC FIELD
V.T. Adonkin1, B.M. Gorelov1, V.M. Ogenko1, V.S. Melnikov2,
I.B. Kevdina3, V.P. Shantorovich3, and G.M. Shalyapina4
1Institute of Surface Chemistry, National Academy of Sciences,
Gen. Naumov Str. 17, 03680 Kyiv-164, UKRAINE
2Institute of Geochemistry, Mineralogy and Oreformation, 03164 Kyiv, UKRAINE
3Institute of Chemical Physics, 117977 Moscow, RUSSIA
4Research Institute of Applied Physics, 140005 Moscow, RUSSIA
Abstract
In YBa2Cu3O7-δ high temperature superconductors with δ<0.3 the irradiation by super
high-frequency electromagnetic field with impulse power 104-106 W gives rise to a decrease
of the rates of annihilation and capture of positrons, a growth of resistance, residual
resistance, thermopower and the block of diffusive transitions of Au atoms, which are caused
by the subthreshold defect formation in the intermediate layers. The irradiation effect is
enhanced with rise of the number of defects in samples and does not depend on an impulse
power. The defect formation is related to the excitation of low-frequency weakly damped
collective excitations under irradiation, whose propagation through the crystal is accompanied
by the Coulomb ejection of atoms from the lattice sites and the transformation and transport
of defects.
Introduction
In high temperature superconductors the plasmon mechanism of superconductivity
may be realized at presence of the low-frequency collective excitations [1, 2]. The
subthreshold defect formation in the intermediate layers is the feature of such excitations and
may indicate the exhibition of the low-frequency plasmons [3]. The low-energy subthreshold
defect formation in the field of plasmons, when the energy of excitations E«Ed and the time of
atomic displacement τ≥ 1-
Dv »τd (Ed, τd are the threshold energy and time of atomic
displacement for the impact defect formation due to elastic collisions with particles having the
overthreshold energy, ωD is the Debye frequency) [4], is possible if the antinodes of the
charge density of excitations is strongly localized on atoms and the localization time for
charge antinodes on the lattice ions τ£T (T is the period of collective excitations) is sufficient
to push out them into interstices to the distance, excluding the defect recombination, or when
the frequency of excitations is
Ωq= qu £ ωD (1),
where q, u are the wave vector and velocity of excitations. Since the energy of collective
vibrations of the carriers in the cuprate layers (the light l-carriers), in the bands B1 built
dp-orbitals of Cu2, O2, O3 atoms [5, 6], is ћΩl=1.3-2.8 eV [7], the plasma frequency is Ωl»ωD
(ћωD≈0.05 eV [8]), and the subthreshold defect formation with participation of the l-carriers is
improbable. In YBa2Cu3O7-δ the energy of plasmons moving along the c axis is 10-40 meV
[9], hence the condition for the subthreshold creation of defects is correct for such excitations.
Along the c axis it is possible the propagation of carriers (the heavy h-carriers) localized in
70
the band formed by dp-orbitals of Cu1, O1, O4 and Cu2 atoms (B2 band). The propagation
along the c axis of carriers localized in B1 and B3 band which is created by dp-orbitals of
Cu1, O4, O1 atoms and has the vacant character is improbable [5, 6].
In normal conditions the low-frequency collective excitations are created owing to
effects of the local field [1, 2], however the subthreshold defect formation is not realized due
to the Landau damping of plasmons on l and h-carriers and the low number of weakly damped
plasmons. To increase the number of weakly damped excitations and to enhance the
subthreshold defect formation the external super high-frequency (SHF) electromagnetic field
can be used. Under action of the SHF electric field ,sin tovoEE = when lho ,uv << ( lh,u are
the collision frequencies of l and h-carriers) the l and h-carriers localized in the
quasi-two-dimension bands with the different dispersion laws and effective masses **
lh mm >>
acquire the various velocities
t
m
et o
lholh
lh v
uv
cos)(
,
*
,
,
~
oEv -= . (2)
The Landau damping on the l-carriers weakens as the field amplitude and the velocities of
carriers rise. When the Fermi velocities of h and l-carriers is )()(
~~
tt lh FF vv << , the collective
excitations with modes having the phase velocity
)()(
~~
tt lh FF vuv <<<< (3),
may propagate without dissipation through the crystal with creation of defects. Note that the
effect of SHF irradiation can not directly give rise to the formation, transport and
transformation of defects, since the quantum energy of SHF field is neglectly low in contrast
to the displacement energy Ed>20 eV for Y, Ba, Cu atoms, Ed≥4.5 eV for O1, O2, O3 atoms
[10-12] or their migration energy.
In the present work the subthreshold defect formation under action of SHF irradiation
was investigated in YBa2Cu3O7-δ superconductors. The investigations were performed by
positron lifetime spectroscopy, X-ray structural analysis, dc resistivity, thermopower and
diffusion of radioactive tracers. Positron spectroscopy was used for determination of the
electron density in the intermediate layers, where inYBa2Cu3O7-δ positrons annihilate [13]. To
control the lattice parameters a, b, c and parameter η= (CO1-CO5)/(CO1+CO5), where CO1,
CO5 are the concentrations of oxygen atoms in O1 and O5 sites [14], X-ray diffraction was
used. The influence was studied of defect formation in the Ba-O, Cu1-O layers on dc
resistivity, thermopower and diffusive transitions of gold atoms.
Samples and experimental details
The YBa2Cu3O7-õ X-ray single-phase polycrystalline samples with δ≤ 0.3 and density
5.5 g/cm3 were investigated. Sintered samples were prepared by solid-phase synthesis [3]. The
nonstoichiometric compounds with δ>0 were obtained by annealing of samples with δ=0 in
vacuum. The amount of oxygen was determined using Q-1500 derivatograph and X-ray
diffraction. Samples for investigations were prepared from the same polycrystalline block.
Samples were irradiated by impulsive SHF electromagnetic emission with impulse
powers P=106 W, frequency 3.0 GHz, duration 2.5 μs, repetition frequency 350-400 Hz and
P=104 W, frequency 9.4 GHz, duration 2.5 μs, repetition frequency 400 Hz at room and
nitrogen temperatures Tr. Samples were situated in the antinode of SHF electrical field in the
reentrant resonator.
71
The positron lifetime annihilation spectra were measured using “ORTEC”
spectrometer at room temperature. The positron annihilation rate λf and capture rate υ were
determined from expressions
λf = I1/τ1 +I2/τ2 , υ= I2(1/τ1 –1/τ2), (4)
where I1, I2 and τ2 , τ1 are the intensities and positron lifetimes in the quasi-free and bound states.
X-ray structural analysis was done on DRON-2 and ADP-1 diffractometers. The parameter η
was determined from ratio of structure amplitudes of the 102 and 012 reflections [14]. The
measurements of annihilation and lattice parameters were carried out on the same samples.
Resistance was measured by four-probe method. Thermopower was measured with copper
contacts when the temperature gradient on sample was 0.5-1.5 K.
The diffusion coefficient of gold atoms was measured by the layer removal method using
radioactive tracers 195Au. The diffusion profiles development in an air environment in the temperature
interval 200-500oC for 5-45 h and were determined with a step size of 3-5 μm to a depth of 150-250
μm.
Experimental results and discussions
The positron lifetimes and the lattice parameters of YBa2Cu3O7-õ samples prior and after SHF
irradiation with P=106 W, ωo=3.0 GHz are listed in the Table. At 293 and 77 K the SHF irradiation
gives rise to a growth of τ1 and τ2; moreover after irradiation the τ2 exceeds the value 500 ps which is
typical for annihilation in the large vacancy clusters or on the surface [15]. The irradiation effect is
distinctly manifested in behavior of the rates of annihilation and capture of positrons (Fig. 1). The
dependencies of λf(t) and υ(t) are similar. In both compounds λf and υ abrupt lower after irradiation
for 1 min. With rise of irradiation time the changes in λf and υ weaken and for t>5 min parameters are
insignificantly varied.
Table. Parameters of positron annihilation, crystal lattice and vacancy clusters
Samples Tr,
K
t,
min
τ1, ps I1,% τ2, ps I2, % c, Å
η
N+×
1 10-15,
cm-3
r+,
Å
YBa2Cu3O7
YBa2Cu3O6.7
293
77
293
77
0
1
5
30
0
1
5
10
30
0
1
5
30
0
1
5
169±2
195±1
188±2
186±2
169±2
184±3
183±3
180±2
179±1
180±2
197±1
199±2
194±2
180±2
196±2
198±2
83±1
97±1
96±2
92±1
83±1
91±1
92±1
90±2
84±3
86±2
97±1
95±1
96±1
86±2
96±1
96±1
331±27
540±39
510±31
385±31
331±27
360±37
363±51
366±24
302±26
341±24
593±57
438±67
469±47
341±24
491±69
476±55
17±1
3±1
4±2
8±1
17±1
9±1
8±1
10±2
16±3
14±2
3±1
5±1
4±1
14±2
4±1
4±1
11.667
11.668
11.645
11.645
11.667
11.660
11.642
-
-
11.715
11.677
11.677
11.705
11.715
11.660
11.660
0.09
0.36
0.35
0.05
0.09
0.15
0.46
-
-
0.35
0.60
0.60
0.44
0.35
0.03
0.03
13
2.7
3.4
5.5
13
6.2
5.8
7.0
10
11
2.3
3.4
3.6
11
3.3
2.6
3.0
3.4
3.0
3,2
3.0
3.1
3.0
3.2
2.7
2.7
3.3
3.2
2.9
2.7
2.8
3.2
72
Fig. 1. The rates of annihilation (a) and capture (b) of positrons as function of SHF irradiation
time with impulse power 106 W at 293 and 77 K in YBa2Cu3O7-δ with δ=0 (1, 11) and
0.3 (2, 21).
Note that in YBa2Cu3O7 irradiated samples the annihilation rate corresponds to value
of λf in compounds with oxygen deficit 0.3≤δ≤0.45 and Tc=45-60 K [16]. However, the SHF
irradiation does not change the oxygen content in YBa2Cu3O7-õ samples, since in irradiated
and unirradiated samples the curves of mass variation due to loss or absorption of oxygen
upon heating are identical. Besides, in YBa2Cu3O7 irradiated samples the reduction in Tc and
transformation of resistance behavior in the R(T) run, which are typical for compounds with
oxygen deficit 0.3≤δ≤0.45, are not observed. After SHF irradiation of YBa2Cu3O7
superconductors the Tc is not shifted, though at Tc<T≤150 K in the R(T) dependence a growth
of resistance is revealed as T lowers (Fig. 2), which is also observed in samples with the high
number of radiation defects [17]. The effect of SHF irradiation does not depend on the
impulse power, while that is determined by the number of defects in samples and is enhanced
as the amount of defects arises. The multiple irradiation by impulses with P=104 W for
5-15 min leads to the increase in Tc on 0.5-1 K without change in the run of R(T) for shot
times and the reduction in Tc on about 4.5 K, broadening of superconducting transition,
transformation of the R(T) run, when R rises as temperature lowers for t>30-45 min (Fig. 2,
insert a). The enhancement of the SHF irradiation effect is distinctly manifested in samples
with the uncompleted superconducting transition, where the single irradiation for 15 min
essentially arises R in the normal state and the residual resistance at T<Tc, while Tc is not
73
shifted (Fig. 2, insert b).
Fig. 2. Temperature dependencies of resistance in YBa2Cu3O7 prior (1) and after SHF
irradiation with impulse power 106 W for 1 (4), 5 (3), 10 (2) min at 77K. The insets
show temperature variations in the resistance of YBa2Cu3O7 prior (1) and after
irradiation at 293 K with impulse power 104 W under multiple action (a) for 30 (2),
240 (3), 720 (4) min and single action (b) on samples with uncompleted
superconducting transition for 15 min.
The drop in λf and υ accompanied by a decrease of the lattice parameter c, while
parameters a=3.821Ǻ, b=3.889Ǻ for YBa2Cu3O7 and a=3.828Ǻ, b=3.889Ǻ for YBa2Cu3O6.7
are not varied, and the random changes of η in the interval 0.05-0.46, which corresponds to
transitions of 1021 cm-3 oxygen atoms between O1 and O5 sites in the basal plane. The
reduction in c indicates that the possible lattice defects are the metal atoms, whose exit into
interstices or drains decreases the repulsion among lattice layers and may result in
compression of the lattice. The displacement of oxygen atoms from O1, O5 sites is apparently
caused by the subthreshold mechanism, since the energy which carriers acquire in the SHF
field is essentially less than the energy of impact displacement of O1 atoms or the energy of
O1→O5 migration [18].
Thus, under action of SHF irradiation the positron annihilation rate reduces when in
the intermediate layers the oxygen content is constant. The reduction in λf may be ascribed to
the formation of Ba and Cu1 defects and the exit of atoms from the annihilation volume. The
annihilation rate is related to the charge density of electrons n-(r) and positron n+(r) by
expression [19]
lf= ò rd
e
cr 3
2
2
0p
n+(r) n-(r)e[ n-(r)], (5)
where )()()( ,
,
*
, rrr k
k
k l
l
len YY= å- , )()()( * rrr +++ YY=å n
n
nn , )(, rk lY , )(r+Yn are the
electron and positron wave functions, k is the wave vector (k≤kF is the Fermi wave vector), l,
n are the band and positron numbers, 0r , c are the classical radius of electron and light speed,
e[ n-(r)] is the enhancement factor. The electron density in intermediate layers r includes the
density of core electrons of Cu1, Ba, O1, O5, O4 rcore atoms, the electron density in the B2
rB2 and B3 rB3 bands. When the carriers are strongly localized in B2 and the B3 band has a
vacant character, we can write
74
lf= 2
0rp сer » 2
0rp сe(rcore + rB2 + rB3 ) , (6)
where the enhancement factor is given [20]
e(rs)= 1+ 0.1512rs+ 2.414 2/3
sr -2.01 2
sr + 0.4466 2/5
sr + 0.1667 3
sr , (7)
and e=2.3 for rs=(3/4pr)1./3=1 (r=1.6´1024 сm-3).
After UHF irradiation during 1-30 min the changes Dl f=l f (0)- lf (t) are in the
interval 0.18£Dlf £0.40 ns-1, which corresponds the reduction in the electron density
Dr≈(1.1-2.4)·1022 сm-3. The Dr value exceeds the density of free carriers rB1+ rB2+ rB3 ≈5·1021
сm-3 [16], (rB1 is the density of carriers in the B1 band), i.e. Dr>rB1+ rB2+ rB3 and Δρ>rB2+ rB3.
Since rB2 »rB3, we have Dr≈ Δrcore and
Dl f= 2
0rp eDr» 2
0rp eDrcore. (8)
Thus, the reduction in l f is caused by the exit of core electrons of atoms from
annihilation process. In YBa2Cu3O7-δ when δ→0.3 the λf drops as the number of O1 vacancies
arises in Cu-O1 layers. Under SHF irradiation when the oxygen content is unchanged the
vacancies and interstitial atoms of Ba and Cu1 may be by defects whose electrons do not
participate in annihilation. In the interstices the charge of cations repels positrons, decreases
the overlap of )(, rk lY and +Yn (r), prevents to the annihilation with core electrons and
reduces r.
The influence of O4, O1 interstitial defects on lf is improbable. The exit of О4, О1
atoms in interstices may reduce the overlap of )(, rk lY and +Yn (r) wave functions and lf
magnitude. However, if the defects have a negative charge, the noninvolvement of the core
electrons in annihilation is improbable. The oxygen transitions from O1 in O5 sites do not
apparently affect on lf, since oxygen atoms remain in the annihilation volume.
The appearance of Ba and Cu1 vacancies is consistent with reduction of c parameter.
The number of defects of Ba and Cu1 atoms nd≈Δρ/ne can be estimated assuming that the
average number of core electrons which does not participate in the annihilation is ne=45. Then
nd equals ~(2.4-5.3)·1020 cm-3. The obtained values of nd are probably understated, since the
deep core electrons of defects are not involved in the annihilation. However, the subthreshold
mechanism of defect formation is evident, since the displacement energy of Ba and Cu1
atoms from the lattice sites is 20-25 eV that excludes the defect formation directly under
action of SHF irradiation. Besides, the ejection of atoms is caused by the collective
excitations of h-holes, because the SHF irradiation cannot create the long-lived holes on the
deep levels of atoms, in whose field the defect formation may take place, due to the low
energy of quantum. Note that the subthreshold defect formation is not apparently realized in
the cuprate layers, where the modulate field of collective excitations of h-carriers is screened
by the l-carriers.
The lifetime of positrons captured by defects essentially exceeds the values
τ2=160-280 ps, which characterize the positron annihilation with the single defects or Cu1-O1
bivacancies in YBa2Cu3O7-õ [21], and indicates that the vacancy clusters are the positron
traps. The υ(t) behavior shows that transformation of clusters takes simultaneously place with
formation of the single defects. Since the capture rate [22]
u= 4pr+D+ ò
¥
+ »
r
dRRRP )( 4πr+D+N+, (9)
where r+ , N+ = ò
¥
+
r
dRRP )( are the radius and concentration of vacancy clusters, P+(R) is the
function of defect distribution in radius, r is the minimum radius when positrons are captured
75
by traps, D+ is the diffusion coefficient of positrons and in approximation of the spherical
symmetry the trap radius is [23]
r+ = [x2 (1+y)2 /(2mU/ h 2 )]1/2 , (10)
where m is the electron mass, U is the depth of the potential well of defects, h is Plank’s
constant, х=1/у[lft2/((1+y2)-1)], x=p-arctg1/y. Assuming that U=2 eV [21],
D+=0.1 сm2/s [24] in the initial samples we can get r+ =2.7-3 Å, N+=(1.1-1.3)·1016 сm–3 (see
the Table), i.e. the traps are vacancy clusters consisting of 6-10 point vacancies. The SHF
irradiation enhances the association and dissociation reactions of clusters in normal and
superconducting states of YBa2Cu3O7-õ superconductors. For shot irradiation time t≤5 min the
number of clusters reduces in ~2.4-5.3 times, while the radius of clusters, as rule, arises. The
rise of r+ indicates the association of single vacancies and clusters, and the reduction in N+
may be caused by the partial healing of clusters, their dissociation or recombination on the
surface. Since the changes in N+ and r+ are accompanied by reduction in ρ, the formation of
Ba and Cu1 vacancies simultaneously occurs with transformation of clusters. Note that the
recombination of clusters on the surface is improbable due to high activation energy of cluster
migration.
When t>5 min the N+ and ρ arise, r+ is altered with increase of irradiation time. This
may be ascribed to the association of Ba, Cu1, O5, O1 single vacancies in clusters. From the
other side, the changes in N+ and r+ may be evidence that SHF irradiation enhances the defect
migration in the crystal bulk.
Since nd»N+, the changes in R(T) is apparently caused by the Ba, Cu single defects
created in the intermediate layers. The transformation of R(T) run, growth of residual
resistance, width of superconducting transition show a formation of the high number of
defects under action of the SHF field. The appearance of defects leads to a decrease of the
relaxation time of l-carriers on defects τd and if in the interval T>Tc [2]
R(T)= [ ])()(4 11
2 TTrr phd
l
qg
p
++
W
-- , (11)
where τph is the relaxation time on phonons, the R growth with decreasing temperature is
caused by the predominant dissipation on defects in the range Tc<T<240 K, where
)},()([ 11 TTr phd qgt +> -- when the dissipation time on phonons 1-
pht ~T and the Landau
damping of collective excitations on h-carriers (γq~T and γq~T2 for the nondegenerate and
degenerate carriers) are reduced.
The non-monotonous shift of the critical temperature in YBa2Cu3O7 is apparently
caused by a rise of the number of holes in the cuprate layers responsible for high temperature
superconductivity, since Tc is related to the hole concentration p by relation [25]
Tc(p)= Tcm[1-82.6(p-0.16)2], (12)
where Tcm is the maximum value of Tc. Under SHF irradiation the smooth entering of holes
in the CuO2 layers caused by the hole redistribution among layers when the electron density
lowers and p arises in the intermediate layers may result in the increase of Tc to Tcm for shot t,
and the reduction in Tc with growth of t and p in the intermediate layers.
From the other side, when the hole redistribution among the B1, B2 bands occurs the
behavior of the critical temperature [2]
Tc= ))]1(/()1(exp[ *
~
lmll +-+-W c , (13)
where
~
W is the average frequency of plasmons, *
cm is the Coulomb potential
1
~
F
00* )]/Eln(1[ -W+= ccc mmm ,
l is the coupling constant
76
l= 0
0
1-
c )( Im)(VN(0)2
cc
d
mmwe
w
w
p
-= ¥
¥
ò ,qq ,
¥
cm =N(0)<4pe2/q2>, Vc(q)=4pe2/e(q,w)q2,
EF is the Fermi energy, N (0) is the density of l-carriers at the Fermi level, may be ascribed to
the reduction in
~
W frequency with weakening of the Coulomb repulsion and
pseudopotential *
cm , whose competition leads to the non-monotonous behavior of Tc due to a
decrease of the plasma frequency of h-carriers *22 /4 hh mnep=W as the number of carriers nh
in the B2 band lowers after formation of Ba and Cu1 vacancies. Note, the slight shift of Tc
when the number of defects in the cation sublattice is anomalously high may be evidence that
the reduction in ρ is caused by exit of the core electrons of Ba and Cu1 atoms from the
annihilation when in the oxygen sublattice the defect formation, excluding O1↔O5
transitions, is absent, since the influence of cation defects on Tc is essentially less than the
effect of oxygen defects [26].
Fig. 3. Thermopower as function of temperature in YBa2Cu3O7-δ samples with δ=0 (a) and
δ=0.2 (b) prior (1) and after single SHF irradiation with impulse power 104 W at
293 K for 5 (2), 15 (3), and 45 (4) min. The inserts show the run of ST as a function of
T2.
77
The creation of high defect concentration under action of SHF irradiation is
manifested in temperature dependencies of thermopower and diffusion coefficient of gold
atoms. SHF irradiation of YBa2Cu3O7-õ samples with δ=0 (Fig. 3, a) and δ=0.2 (Fig. 3, b)
gives rise to an increase of S and maximum of S(T) in the interval 100<T<160 K, which is
spread and shifted in side of high temperatures with t growth. Besides, in YBa2Cu3O6.8
samples Tc arises with increasing time to 82 K (t=15 min) and then lowers to 80 K (t=45 min).
The rise of thermopower is related to the growth of an amount of defects, since the analogous
run of S(T) is observed upon introduction of radiation defects [27]. The maximum of S(T) is
probably caused by the phonon drag effect [27,28]. In the cuprate superconductors [29]
S(T)= Sd (T)+ Sph(T)= ( ) å D÷
ø
ö
ç
è
æ
¶
¶-
+÷
ø
ö
ç
è
æ
¶
¶ ,
T/
2ln
3e
T22
uvN
V
ek
qj
EF
a
tse
sp (14),
where Sd, Sph are the diffusive and related to the phonon drag components of S, σ, V are the
tensor of conductivity and the volume of material, N is the density of phonon states with
momentum q in j branch, u is the phonon velocity, τ is the phonon-electron relaxation time,
Dv is the change of electron velocity due to the phonon adsorption. Since σ~T-1,
(»
dT
dN )sin/)( 2 XXk
wh
, here X= ћω/2kT, we have Sph =bT-1 (b is the constant). Assuming
Sd=αT (α is the constant) we get S~aT+ bT-1. The dependencies ST(T2) are linear in the range
T≥150 K (insert in Fig. 3) that is consistent with a phonon contribution in thermopower. In
accordance with relation (14), the rise of S and the S(T) maximum are caused by reduction in
the σ, τ and growth of the Sph contribution due to formation of the high number of defects
under SHF irradiation. The free path of carriers and phonons reduces with increasing
irradiation time that results in the less contribution of Sph and spreading of the S(T) maximum.
Temperature dependencies of the diffusion coefficient of gold atoms are shown in
Fig. 4. In initial samples the diffusion is characterized by slow and rapid components of the
surface diffusion (in cm2/s) in the temperature interval 200-410 oC
s
sD =2.8´10-11exp(-0.072/kT) and r
srD =1.9´109exp(0.13/kT), (15)
and by a volume component [30], which is observed at thermodesorption of O1 atoms when
T≥ 410 oC
s
vD =6.6 exp(-1.24/kT) and r
vD =1.9´10-2 exp(-1.08/kT). (16)
The action of SHF irradiation gives rise to the blocking of volume transitions of Au
atoms and the suppression of both components of rs,
vD , though the irradiation does not effect
on the oxygen desorption. The activation energy and preexponential factor of surface
diffusion coefficients rise, and in the temperature range 200-305 oC the surface diffusion is
described by expressions
s1
sD =8.0´10-10exp(-0.17/kT) and r1
sD =1.8´10-7exp(-0.18/kT), (17)
while at T≥305 oC that is
s2
sD =2.3´10-7exp(-0.45/kT) and r2
sD =2.0´10-6exp(-0.30/kT), (18)
(Fig. 4, curves 2, 2’). The components of surface diffusion s
sD and r
srD have the close values
of activation energy which are essentially less than the values of activation energy in Dv and
do not depend on the number of oxygen in Cu1-O layers. The block of volume diffusive
transitions indicates the enhancement of defect formation in the bulk and the accumulation of
a high amount of defects in the surface layer of crystals under UHF irradiation.
The suppression of volume diffusion, which may be described by expression
Dv=Do(1-q)exp(-E/kT), where q=m/M , m is the number of occupied interstices, M is the total
number of interstices, is caused by a rise of factor q and the blocking of volume transitions as
78
in the surface layer of crystallites the interstices are occupied by defects, i.e. Dv→0 when
q→1.
The increase of preexponential factor of sr,
sD may be ascribed to occupation of the interstices
by defects.
In the case of diffusion with two types of interstices, when [31]
sr,
sD = wa 2l )/exp(2 kTE
q
Kq
-÷÷
ø
ö
çç
è
æ -+
m
ml , (19)
where α is a geometrical factor, l is the jump length, ω is the vibration frequency of atom in
an interstices, μ=1-ε, l=1+2e, K= ( ) mml q1231 2 -+ , )/)exp[( kTuu To -=e , ,ou Tu are
the potential energy of an atom in various interstices, the increase of pre-exponential barriers
ou and Tu .
In case of diffusion transitions from a node at an interstice when [32]
sr,
sD = )/exp()(
6
1 2/12 kTEgl zg --tt , (20)
where g is the number of vacant nodes, ,gt zt are the residence time at a node and at an
interstices, the behavior of s
sD and r
sD can be related to a decrease of gt and zt when defects
occupy interstices and a rise of g due to formation of defects under irradiation.
Fig. 4. Diffusion coefficient of Au atoms as function of temperature in YBa2Cu3O7 samples
prior (1,11) and after 10 (2, 21) min of SHF irradiation with impulse power 104
W
at 293 K.
The blocking of volume diffusive transitions indicates the accumulation of the high
number of defects within the surface layer of crystals. Such defect distribution in the crystals
testifies to the defect transport in the crystal bulk under SHF irradiation. Besides, the defect
accumulation within the thick surface layer may give rise to reduction in λf. If the layer
thickness is less than the diffusion length of positrons the major part of positrons annihilate in
79
the crystal bulk where after irradiation the number of Ba and Cu atoms and the electron
density are lower than in the initial samples.
Thus, the SHF irradiation of YBa2Cu3O7-õ high temperature superconductors with
δ≤0.3 in normal and superconducting states enhances the subthreshold formation of defects in
the intermediate layers, such as vacancies and interstitial atoms of Ba, Cu1 and O1↔O5
transitions, that leads to lowering of the electron density in the intermediate layers, a
redistribution of holes among the cuprate and intermediate layers, a rise of resistance and
thermopower in the normal phase and residual resistance, width of the superconducting
transition. The defect formation is apparently accompanied by the defect transport, which
results in the transformation of vacancy clusters and blocking of the volume and surface
diffusion transitions of Au atoms due to the atomic accumulation within the surface layer of
crystals. Besides, an intensity of the subthreshold defect formation does not depend on the
irradiation power and is enhanced with growth of the number of defects in samples.
The independence of irradiation effect from impulse power may be ascribed to the
realization of condition of the non-dissipation propagation of excitations [1, 2]
2/1
*
*
34 ÷÷
ø
ö
çç
è
æ
=
W lh
hl
nm
nmpg
q
q <<1, (21)
where nl is the concentration of l-carriers, in the interval of impulse power 104-106 W, where
)()(
~~
tt lh FF vv << , and the Landau damping on l-carriers qg is low. The enhancement of defect
formation with growth of the number of defects in YBa2Cu3O7 samples may be ascribed to a
rise of the Drude dissipation and a decrease of plasmon mobility that leads to an increase of
the time interval for interaction of the charge antinodes of collective excitations with atoms
and pushing out them into interstices.
The subthreshold pushing out of Ba, Cu, O1 atoms indicates an existence of the low-
frequency hole collective excitations in the B2 band, whose localization time on atoms is
about .1-
Dw Such excitations are enhanced under action of SHF field due to the nonuniform
heating of carriers in the B1 and B3 bands and weakening of the Landau damping on carriers
in the B1 band. The SHF irradiation weakens the Landau damping and enhances the
propagation of weakly damped collective excitations through the YBa2Cu3O7-õ crystals. The
positive charged Ba and Cu atoms are pushed out into interstices by moving holes, which are
predominantly localized at oxygen atoms, whose p-orbitals make the major contribution to
pd-hybrid orbitals of the B2 band, due to the interaction of antinodes of the hole density with
atoms. The oxygen O1↔O5 transitions and their random character are probably caused by
the mutual repulsion of charge antinodes on the neighboring oxygen atoms. The
transformation of vacancy clusters and the defect accumulation near the surface apparently is
a result of the defect transport in the field of moving excitations through the crystal, when the
association and dissociation of defects and their accumulation near the surface, where
plasmons are scattered, are possible.
Conclusions
In YBa2Cu3O7-δ high temperature superconductors with δ≤0.3 the SHF irradiation,
which does not directly create the lattice defects or the local hole excitations on the deep
levels of atoms, enhances the subthreshold defect formation in the intermediate layers which
is accompanied by the defect transport through the crystals and the defect accumulation near
the crystal surface. The defect formation and atomic transport may be realized in the
modulated field of low-frequency collective excitations propagating along the c axis. The
enhancement of excitations is probably caused by non-uniform heating of carriers in the
various bands.
80
References
1. Pashitskii E.A. Low-frequency excitations of charge density // Fiz. Nizk. Temp. -1985. -
V.21. - P.995-1019.
2. Pashitskii E.A. Low-frequency excitations of charge density // Fiz. Nizk. Temp. -1985. -
V.21. - P.1091-1137.
3. Gorelov B.M. Collective defect formation in the high-temperature superconductor
YBa2Cu3O7 under the influence of adsorbed water molecules // Zh. Eksp. Teor. Fiz. -
1999. - V.89. - P.311-327.
4. Klinger M.I., Lushchik Ch.V., Mashovets T.V., and Sheinkman M.K. Defect formation in
the solid states due to relaxation of electron excitations // Usp. Fiz. Nauk. -1985. - V.147.
- P.521 -563.
5. Bozovic I. Plasmons in cuprate superconductors // Phys. Rev. B. - 1990. - V.42. -
P.1969-1984.
6. Veal B.W. and Chun Gu. Photoemission studies of valence bands in YBa2Cu3O7-δ //
J. Electr. Spectroscopy and Related Phenomena. - 1994. - V.66. - P.321-357.
7. Anderson O.K., Jepsen D., Liechtenstein A.J., and Mazin J.J. Plane dimpling and saddle-
point bifurcation in the band structure of optimally doped high-temperature
superconductors: A tight binding model // Phys. Rev. B. - 1994. - V.49. - P.4145-4157.
8. Wang O., Saunders S., Almond D.P., Cancurtanau M., and Koretta K.C. Elastic and
nonlinear acoustic properties of YBa2Cu3O7-δ ceramics with different oxygen content //
Phys. Rev. B. - 1995. – V.53. - P.3711-3725.
9. Yujao Zho, Cooper S.L., and Pines D. Model of c-axis resistivity of high Tc-cuprates //
Phys. Rev. B. - 1996. - V.53. - P.8253-8256.
10. Baetzold R.C. Atomistic simulation of ionic and electronic defects in YBa2Cu3O7 // Phys.
Rev. B. - 1988. – V.38. - P.11304-11312.
11. Kirsanov V.V., Musin N.N., and Shamarina E.I. Threshold distortion energies in HTSC //
Sverkhprovodimost: Fiz., Khim., Tekh. - 1994. - V.7. - P.427-435.
12. Degtyarenko N.N., Elesin V.F., and Melnikov V.L. Calculation of partial displacement of
HTSC atoms under action of high-energy particles // Sverkhprovodimost: Fiz., Khim.,
Tekh. - 1990. - V.3. – P.2299-2301.
13. Turelic P., Wach A.L., Welzler R.K., Kaiser J.H., West R.N., Jean J.C., and Howell R.H.
Electron momentum studies in high Tc materials by positron annihilation spectroscopy:
theory and experiment // J. Phys. Condens. Matter. - 1990. - V.2. - P.1635-1658.
14. Lysenko V.N., Adonkin V.T., Levchenko V.V., Melnikov V.S., Ogenko V.M., and
Shantorovich V.P. Ultrasonically stimulated ordering effect in the Y-Ba-Cu-O system //
Superconductivity. - 1990. – V.5. – P.341-344.
15. Maninen M., Nieminen R., Hautoiarvi P., and Apronen J. Electrons and positrons in metal
vacancies // Phys. Rev. B. - 1975. - V.12. - P.4012-4022.
16. Ginzberg D.M. Physical properties of high temperature superconductors. Singapore:
World Scientific, 1989.
17. Kar’in A.E., Davydov S.L., Mirmilshtein A.V., Goshchitski B.N., and Sadovskii V.A.,
Wolker Single crystals disordering of neutron irradiation // Sverkhprovodimost: Fiz.,
Khim., Tekh. - 1992. - V.5. - P.2215-2234.
18. Baetzold R.C. Atomistic study of defects in YBa2Cu3O7 // Phys. Rev. B. - 1990. –V.42. -
P.56-66.
19. Boronski E. and Nieminen R.N. Electron-positron density function theory // Phys. Rev. B.
- 1985. – V.34. - P.3820-3831.
20. Stern P.A., Kaiser J.H., O’Brien J., and Howel R. Positron lifetime in solids from first
principles calculations // Mat. Sci. Forum. - 1992. - V.105-110. - P.469-476.
81
21. Jensen K.O., Nieminen R.M., and Pushka M.J. Positron states in YBa2Cu3O7 // J. Phys.
Condens. Matter. - 1989. - V.1. – P.3727-3732.
22. Alexanjan G.G., Berlin A.A., Goldanskii A.V., Grineva N.S., Onistchuk V.A., and
Shantorovich B.P. Study of effects of annealing and plastic deformation in microstructure
of polyarthrit by positron annihilation // Khim. Fiz. - 1986. - V.9.-P.1225-1234.
23. Bulenkov P.A., Zherdev Ju.V., Lapin V.V., Onistchuk V.A., and Shantorovich V.P. Study
of polymer structure by positron annihilation // Khim. Fiz. - 1983. – N 1. -P.126-128.
24. Swiatkowski W. Dyfusia positronov w metalu i efecty uwarunkovane tym procesem //
Acta Universitatis. Matematyka, Fizyka, Astronomia. - 1982. – N 39. - P.3-96.
25. Williams G.V.M., Tallon J.L., Michalak R., and Dupree R. NMR evidence for common
superconductivity and pseudogap phase diagrams of YBa2Cu3O7 and La2-xSrxCaCu2O6 //
Phys. Rev. B. - 1996. – V.54. - P.6909-6912.
26. Roth C., Heeger G., and Schweiss P. Copper defficiency in YBa2Cu3O7-δ // Physica C. -
1988. – V.152. - P.329-334.
27. Uher C. and Huang W.N. Thermoelectric power and thermal conductivity of neutron
irradiated YBa2Cu3O7 // Phys. Rev. B. - 1989. – V.40. – P.2694-2697.
28. Ouseph P.J., Ray M., O’Brayan M., and Ray J. Thermoelectric power of YBa2Cu3O7 //
Phys. Rev. B. - 1990. – V.41. – P.4123-4125.
29. Tradahl H.J. Thermopower of the superconducting cuprates // Phys. Rev. B. - 1995. –
V.51. – P.6175-6178.
30. Alfeev V.N., Gorbic P.P., Dyakin V.V., Ogenko V.M., and Shalyapina G.M. Duffision of
gold in YBa2Cu3O7-δ and (BixPb1-x)2Ca2Sr2Cu3Oy ceramics // Dokl. AN UkSSR. - 1991. -
N1. – P.41-43.
31. Smirnov A.A. Theory of Diffusion in Implantation Alloys. Naukova Dumka: Kiev, 1982
(in Russian).
32. Seith W. Diffusion in Metallen. Springer Verlag: Berlin, 1939.
|
| id | oai:ojs.pkp.sfu.ca:article-84 |
| institution | Surface |
| keywords_txt_mv | keywords |
| language | English |
| last_indexed | 2025-07-22T19:30:09Z |
| publishDate | 2002 |
| publisher | Chuiko Institute of Surface Chemistry National Academy of Sciences of Ukraine |
| record_format | ojs |
| resource_txt_mv | surfacezbircomua/1f/9fefa8d2df93ec669a8b1b39abd1f41f.pdf |
| spelling | oai:ojs.pkp.sfu.ca:article-842018-11-27T09:42:19Z Subthreshold defect formation in YBa 2Cu 3 O7-δ at nonuniform heating of electron gas in electromagnetic field Subthreshold defect formation in YBa 2Cu 3 O7-δ at nonuniform heating of electron gas in electromagnetic field Subthreshold defect formation in YBa 2Cu 3 O7-δ at nonuniform heating of electron gas in electromagnetic field Adokin, V. T. Gorelov, B. M. Ogenko, V. M. Melnikov, V. S. Kevdina, I. B. Shalyapina, G. M. In YBa2Cu3O7-δ high temperature superconductors with δ&lt;0.3 the irradiation by super high-frequency electromagnetic field with impulse power 104-106 W gives rise to a decrease of the rates of annihilation and capture of positrons, a growth of resistance, residual resistance, thermopower and the block of diffusive transitions of Au atoms, which are caused by the subthreshold defect formation in the intermediate layers. The irradiation effect is enhanced with rise of the number of defects in samples and does not depend on an impulse power. The defect formation is related to the excitation of low-frequency weakly damped collective excitations under irradiation, whose propagation through the crystal is accompanied by the Coulomb ejection of atoms from the lattice sites and the transformation and transport of defects. In YBa2Cu3O7-δ high temperature superconductors with δ&lt;0.3 the irradiation by super high-frequency electromagnetic field with impulse power 104-106 W gives rise to a decrease of the rates of annihilation and capture of positrons, a growth of resistance, residual resistance, thermopower and the block of diffusive transitions of Au atoms, which are caused by the subthreshold defect formation in the intermediate layers. The irradiation effect is enhanced with rise of the number of defects in samples and does not depend on an impulse power. The defect formation is related to the excitation of low-frequency weakly damped collective excitations under irradiation, whose propagation through the crystal is accompanied by the Coulomb ejection of atoms from the lattice sites and the transformation and transport of defects. In YBa2Cu3O7-δ high temperature superconductors with δ&lt;0.3 the irradiation by super high-frequency electromagnetic field with impulse power 104-106 W gives rise to a decrease of the rates of annihilation and capture of positrons, a growth of resistance, residual resistance, thermopower and the block of diffusive transitions of Au atoms, which are caused by the subthreshold defect formation in the intermediate layers. The irradiation effect is enhanced with rise of the number of defects in samples and does not depend on an impulse power. The defect formation is related to the excitation of low-frequency weakly damped collective excitations under irradiation, whose propagation through the crystal is accompanied by the Coulomb ejection of atoms from the lattice sites and the transformation and transport of defects. Chuiko Institute of Surface Chemistry National Academy of Sciences of Ukraine 2002-06-12 Article Article application/pdf https://surfacezbir.com.ua/index.php/surface/article/view/84 Surface; No. 7-8 (2002): Chemistry, Physics and Technology of Surface; 69-81 Поверхность; № 7-8 (2002): Химия, физика и технология поверхности; 69-81 Поверхня; № 7-8 (2002): Хімія, фізика та технологія поверхні; 69-81 3154-8091 3154-8083 en https://surfacezbir.com.ua/index.php/surface/article/view/84/83 Авторське право (c) 2002 V.T. Adonkin, B.M. Gorelov, V.M. Ogenko, V.S. Melnikov, I.B. Kevdina, V.P. Shantorovich, G.M. Shalyapina |
| spellingShingle | Adokin, V. T. Gorelov, B. M. Ogenko, V. M. Melnikov, V. S. Kevdina, I. B. Shalyapina, G. M. Subthreshold defect formation in YBa 2Cu 3 O7-δ at nonuniform heating of electron gas in electromagnetic field |
| title | Subthreshold defect formation in YBa 2Cu 3 O7-δ at nonuniform heating of electron gas in electromagnetic field |
| title_alt | Subthreshold defect formation in YBa 2Cu 3 O7-δ at nonuniform heating of electron gas in electromagnetic field Subthreshold defect formation in YBa 2Cu 3 O7-δ at nonuniform heating of electron gas in electromagnetic field |
| title_full | Subthreshold defect formation in YBa 2Cu 3 O7-δ at nonuniform heating of electron gas in electromagnetic field |
| title_fullStr | Subthreshold defect formation in YBa 2Cu 3 O7-δ at nonuniform heating of electron gas in electromagnetic field |
| title_full_unstemmed | Subthreshold defect formation in YBa 2Cu 3 O7-δ at nonuniform heating of electron gas in electromagnetic field |
| title_short | Subthreshold defect formation in YBa 2Cu 3 O7-δ at nonuniform heating of electron gas in electromagnetic field |
| title_sort | subthreshold defect formation in yba 2cu 3 o7-δ at nonuniform heating of electron gas in electromagnetic field |
| url | https://surfacezbir.com.ua/index.php/surface/article/view/84 |
| work_keys_str_mv | AT adokinvt subthresholddefectformationinyba2cu3o7datnonuniformheatingofelectrongasinelectromagneticfield AT gorelovbm subthresholddefectformationinyba2cu3o7datnonuniformheatingofelectrongasinelectromagneticfield AT ogenkovm subthresholddefectformationinyba2cu3o7datnonuniformheatingofelectrongasinelectromagneticfield AT melnikovvs subthresholddefectformationinyba2cu3o7datnonuniformheatingofelectrongasinelectromagneticfield AT kevdinaib subthresholddefectformationinyba2cu3o7datnonuniformheatingofelectrongasinelectromagneticfield AT shalyapinagm subthresholddefectformationinyba2cu3o7datnonuniformheatingofelectrongasinelectromagneticfield |