Phase transitions in KDP crystals with the complex organic and inorganic impurities
In this paper we present the results of the study of dielectric and thermal properties of KDP crystals doped with different complex organic and inorganic molecules which decorate different (pyramidal or prismatic) crystal growth sectors. It is shown that the properties of stained and transparent par...
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| Zitieren: | Phase transitions in KDP crystals with the complex organic and inorganic impurities / B. Strukov, I. Shnaidshtein, S. Grabovsky // Condensed Matter Physics. — 2007. — Т. 10, № 1(49). — С. 111-118. — Бібліогр.: 21 назв. — англ. |
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Strukov, B. Shnaidshtein, I. Grabovsky, S 2017-05-28T16:14:34Z 2017-05-28T16:14:34Z 2007 Phase transitions in KDP crystals with the complex organic and inorganic impurities / B. Strukov, I. Shnaidshtein, S. Grabovsky // Condensed Matter Physics. — 2007. — Т. 10, № 1(49). — С. 111-118. — Бібліогр.: 21 назв. — англ. 1607-324X PACS: 81.10.Aj, 61.72.Ww, 77.84.Fa, 77.80.Dj, 77.80.Bh DOI:10.5488/CMP.10.1.111 https://nasplib.isofts.kiev.ua/handle/123456789/118071 In this paper we present the results of the study of dielectric and thermal properties of KDP crystals doped with different complex organic and inorganic molecules which decorate different (pyramidal or prismatic) crystal growth sectors. It is shown that the properties of stained and transparent parts of the crystal in comparison with the corresponding parts of the nominally pure crystal are different for KDP crystals grown by means of traditional (slow) and rapid growth technique. The difference of the domain contribution into dielectric constant of the polar phase and its characteristic hysteresis in pure and dyed crystals, transition temperature position, form of the specific heat anomaly are presented and analyzed. The most probable model of incorporation of the complex impurity molecules into KDP structure is proposed. У цiй статтi ми представляємо результати вивчення дiелектричних та термiчних властивостей кристалiв KDP, легованих рiзноманiтними комплексними органiчними та неорганiчними молекулами,якi покривають рiзнi (пiрамiдальнi або призматичнi) дiлянки росту кристалу. Показано, що властивостi зафарбованих i прозорих частин кристалу у порiвняннi з вiдповiдними дiлянками номiнально чистого кристалу є рiзними для кристалiв KDP, вирощених з використанням традицiйної (повiльної) та швидкої технологiй вирощування. Представлено та проаналiзовано вiдмiннiсть доменного вкладу у дiелектричну сталу полярної фази та характерний гiстерезис для чистих i зафарбованих кристалiв, розташування температури переходу та форму аномалiї теплоємностi. Запропоновано найбiльш правдоподiбну модель включення молекул комплексних домiшок у структуру KDP. Authors thank the RFBR for the financial support of this research (project 05-02-16873a), N. Zaitseva and L. Carman for the samples of KDP+CSB and KDP+A crystals, B. Kahr for the samples of KDP+PCR crystals and I. Pritula and Yu. Velikhov for the samples of KDP+XO crystals. The discussions with L. Rashkocich are very much appreciated. en Інститут фізики конденсованих систем НАН України Condensed Matter Physics Phase transitions in KDP crystals with the complex organic and inorganic impurities Фазовi переходи в кристалах KDP з комплексними органiчними та неорганiчними домiшками Article published earlier |
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| title |
Phase transitions in KDP crystals with the complex organic and inorganic impurities |
| spellingShingle |
Phase transitions in KDP crystals with the complex organic and inorganic impurities Strukov, B. Shnaidshtein, I. Grabovsky, S |
| title_short |
Phase transitions in KDP crystals with the complex organic and inorganic impurities |
| title_full |
Phase transitions in KDP crystals with the complex organic and inorganic impurities |
| title_fullStr |
Phase transitions in KDP crystals with the complex organic and inorganic impurities |
| title_full_unstemmed |
Phase transitions in KDP crystals with the complex organic and inorganic impurities |
| title_sort |
phase transitions in kdp crystals with the complex organic and inorganic impurities |
| author |
Strukov, B. Shnaidshtein, I. Grabovsky, S |
| author_facet |
Strukov, B. Shnaidshtein, I. Grabovsky, S |
| publishDate |
2007 |
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English |
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Condensed Matter Physics |
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Інститут фізики конденсованих систем НАН України |
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Article |
| title_alt |
Фазовi переходи в кристалах KDP з комплексними органiчними та неорганiчними домiшками |
| description |
In this paper we present the results of the study of dielectric and thermal properties of KDP crystals doped with different complex organic and inorganic molecules which decorate different (pyramidal or prismatic) crystal growth sectors. It is shown that the properties of stained and transparent parts of the crystal in comparison with the corresponding parts of the nominally pure crystal are different for KDP crystals grown by means of traditional (slow) and rapid growth technique. The difference of the domain contribution into dielectric constant of the polar phase and its characteristic hysteresis in pure and dyed crystals, transition temperature position, form of the specific heat anomaly are presented and analyzed. The most probable model of incorporation of the complex impurity molecules into KDP structure is proposed.
У цiй статтi ми представляємо результати вивчення дiелектричних та термiчних властивостей кристалiв KDP, легованих рiзноманiтними комплексними органiчними та неорганiчними молекулами,якi покривають рiзнi (пiрамiдальнi або призматичнi) дiлянки росту кристалу. Показано, що властивостi зафарбованих i прозорих частин кристалу у порiвняннi з вiдповiдними дiлянками номiнально чистого кристалу є рiзними для кристалiв KDP, вирощених з використанням традицiйної (повiльної) та швидкої технологiй вирощування. Представлено та проаналiзовано вiдмiннiсть доменного вкладу у дiелектричну сталу полярної фази та характерний гiстерезис для чистих i зафарбованих кристалiв, розташування температури переходу та форму аномалiї теплоємностi. Запропоновано найбiльш правдоподiбну модель включення молекул комплексних домiшок у структуру KDP.
|
| issn |
1607-324X |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/118071 |
| citation_txt |
Phase transitions in KDP crystals with the complex organic and inorganic impurities / B. Strukov, I. Shnaidshtein, S. Grabovsky // Condensed Matter Physics. — 2007. — Т. 10, № 1(49). — С. 111-118. — Бібліогр.: 21 назв. — англ. |
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2025-11-26T09:52:11Z |
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Condensed Matter Physics 2007, Vol. 10, No 1(49), pp. 111–118
Phase transitions in KDP crystals with the complex
organic and inorganic impurities
B.Strukov, I.Shnaidshtein, S.Grabovsky
Lomonosov Moscow State University, Moscow, 119992, Russia
Received September 4, 2006
In this paper we present the results of the study of dielectric and thermal properties of KDP crystals doped with
different complex organic and inorganic molecules which decorate different (pyramidal or prismatic) crystal
growth sectors. It is shown that the properties of stained and transparent parts of the crystal in comparison
with the corresponding parts of the nominally pure crystal are different for KDP crystals grown by means of
traditional (slow) and rapid growth technique. The difference of the domain contribution into dielectric constant
of the polar phase and its characteristic hysteresis in pure and dyed crystals, transition temperature position,
form of the specific heat anomaly are presented and analyzed. The most probable model of incorporation of
the complex impurity molecules into KDP structure is proposed.
Key words: ferroelectrics, impurities, dielectric constant, dye molecules, specific heat, crystal growth
PACS: 81.10.Aj, 61.72.Ww, 77.84.Fa, 77.80.Dj, 77.80.Bh
1. Introduction
It is well known that KH2PO4 (KDP) crystals represent the most typical hydrogen-bonded
ferroelectric with the order-disorder phase transition. This model crystal was studied more in de-
tail than other ferroelectrics and is the most convenient object for the construction of macro-
and microscopic theories of such transitions [1,2]. Besides, KDP crystals have outstanding nonli-
near optical properties; for some applications in laser optics, very large plates of the crystal were
claimed [3], therefore the methods of rapid growth of KDP-type crystals were successfully devel-
oped [3,4]. At paraelectric phase KDP crystals belong to the point group 42m and are faceted
by the sets of {101} (pyramidal) and {100} (prismatic) faces. For the crystal grown using the
traditional technique with low supersaturation, the growth rate is 0.5–1 mm/day. Here the crystal
grows only in the [001] direction with the quite slow growth of the {100} faces due to the blocking
effect of polyvalent ion impurities in solution on prismatic faces [5]. On the other hand, the crystals
grown with the rate exceeding 10 mm/day (rapid growth technique [3,4]) start from the point seed
and grow uniformly for both prismatic and pyramidal faces since in this case the blocking effect
of inevitable solution impurities becomes much smaller and is distributed more uniformly on all
faces. Surprisingly, optical and nonlinear optical properties of the crystals grown using the rapid
growth technique turn out to be of the same quality as the crystals grown using a traditional
method. It should be noted that the difference in the properties of pyramidal and prismatic sectors
of KDP crystals grown by means of the traditional technique was detected in some experimental
works. For example, the domain pattern is quite different in different sectors revealing the regular
stripes which are parallel to (100) or (010) plane in the pyramidal sector, whereas in the prismatic
sectors the domains width and length are distributed irregularly and are completely restored after
repeatedly passing through Curie temperature [6]. Therefore, only the samples originated from the
pyramidal sectors were considered in the number of works.
Thus, it becomes evident that it is important to identify the “pure” KDP samples obtained
from certain growth sectors before introducing the impurities into the crystal. It is known that
the anomalously high dielectric constant in ferroelectric phase in KDP crystals is a result of a
higher mobility of the domain walls which is extremely sensitive to the presence of different kinds
c© B.Strukov, I.Shnaidshtein, S.Grabovsky 111
B.Strukov, I.Shnaidshtein, S.Grabovsky
of defects [7–9]. In what follows we choose the domain contribution into dielectric constant in the
polar phase as a parameter closely related to the impurity density and defect concentration in the
sample.
The effect of organic dye molecules of hematein in KDP crystal has been originally observed
in [10]. The authors revealed for the first time that this dye can recognize the different faces of
growing KDP crystal staining only every other prism face. They found out that the transition tem-
perature in the doped sectors was depressed by 2 K. Recently it was shown that many other different
dyes and complex inorganic molecules can be introduced in the KDP crystal lattice selectively in
pyramidal or prismatic sectors [11,12] but no information about thermodynamic properties of the
stained and nonstained parts has been reported. The puzzling peculiarity of the case is the lack of
similarity between guest molecules and host crystal structure; in this sense the dye impurities can
be considered as “nonisomorphic” to the crystal lattice and still there is a problem in understanding
the capability of the growing crystal to accommodate such “inconvenient” inclusions violating the
principles of isomorphism and discriminating between different faces. It seems evident that these
partly ordered “inclusions” into piezoelectric inorganic matrix have to develop the local strains
and accompanying local polarization. Therefore, it is possible to create the “strong” polar defects
in ferroelectric crystal and to study their effect on the phase transition. In this paper we present
a short review of our studies of the complex organic and inorganic molecules concerning dielectric
and thermal properties of KDP crystals. The dye staining pyramidal or prismatic sectors of the
host crystal are considered. The difference in the properties of the “pure” KDP crystals grown by
means of traditional and rapid growth techniques is considered as a necessary background for the
separation of defects – induced effects [13].
2. Experimental
The following crystals grown using rapid growth technique were in our disposal: pure KDP,
traditionally and rapidly grown; KDP + organic dye Amaranth (A), KDP + organic dye Chicago
Sky Blue (CSB) – both dyes stain only pyramidal sectors; KDP + organic dye Xylenol Orange (XO),
KDP + inorganic dye Pento-Chloro-Ruthenate (PCR) – both dyes stain only prismatic sectors.
Impurity distributions are represented schematically in figure 1. Spectral analysis revealed the
average concentration of dye molecules as 1–5 molecules of dye at 105 molecules of KDP, average
volume of crystals was about several tens of cm3. All samples were cut perpendicular to the polar c-
axe as plates with the size about 5×8×1 mm3. The thin layers of silver paste was used as electrodes.
For dielectric measurements the automatic capacitance bridge with the typical frequency of 10 kHz
was used. The rate of the sample cooling/heating far from TC was 0.5–1 K/min and 0.1–0.2 K/min
in the vicinity of the transition point. Specific heat data were obtained using a computerized
adiabatic calorimeter in the temperature range 4–160 K. In this case the sample has a form of
cylinder with a diameter 8 mm and height 13 mm. The temperature step was 2 K far from TC and
0.02 K in the vicinity of the transition point. The accuracy of the specific heat measurements was
0.5% and was checked by comparing our data with the classical work [14] at low temperatures.
Figure 1. Schematic presentation of dye molecules incorporated into different growth sectors of
KDP crystal.
112
KDP crystals with the complex impurities
3. Dielectric properties: pyramid-stained crystals
As it was pointed in Introduction (and it will be necessary for the interpretation of the further
results) the initial habitus of the nominally pure KDP crystals is connected with the presence
of polyvalent ions (Cr+3, Fe+3, Al+3, Sn+4) in a solution. It is generally accepted that these
impurities inhibit the growth of the crystal in the [001] direction because they are easily adsorbed
by the prismatic faces and block their growth if the crystal is grown by traditional method from
the slightly supersaturated solution. At the same time, the growth of the pyramidal faces is not
prevented by these impurities. On the other hand, the rapid growth technique makes it possible
to overcome the blocking effect of impurities and to grow the crystal uniformly so that the final
size of the crystal almost does not depend on the initial size of the seed. It is clearly seen in
figure 2 that the temperature dependencies of dielectric constant of KDP crystal grown by both
methods is quite different for different sectors: curve 1 shows the classical picture for the pyramidal
sector of traditionally grown crystal: there is a temperature region in the polar phase where ε
has an anomalously high values (“plateau” region); near 90 K ε sharply decreases, revealing the
“freezing out” of the contribution of domain walls mobility. It is evident from curves 2, 3 that both
the pyramidal and prismatic sectors of the rapidly grown crystal have the following features in
comparison with the previous case: the lower value of ε at TC and a suppressed domain mobility
in polar phase. If we accept that the domain mobility contribution to dielectric constant can be
Figure 2. Temperature dependencies of dielectric constant for the nominally pure KDP crystals
grown using different methods: 1-pyramid (traditional method), 2-pyramid (rapid growth), 3-
prism (rapid growth).
Figure 3. Temperature dependence of dielectric constant of pure KDP (1), KDP+CSB (2), and
KDP+A (3) crystals. (a) – pyramidal sector, (b) – prismatic sector.
taken as a measure degree of the crystal quality, one can conclude from figure 2 that the pyramidal
sector in rapidly grown KDP crystal in one case is more defected than the prismatic one and that
113
B.Strukov, I.Shnaidshtein, S.Grabovsky
the kinetics of the crystal growth determines the impurity distribution between the growth sectors
of the crystal.
Temperature dependence of dielectric constant of pure KDP crystals and KDP crystals with
decorated pyramidal sectors (KDP+CSB and KDP+A) is presented in figure 3. All crystals were
grown using a rapid growth technique. Data for both dyed (pyramidal) and transparent (prismatic)
sectors were inspected. It is seen that the pyramidal sectors of pure and decorated crystals have
got very similar temperature dependencies of dielectric constant; at the same time there is a
striking difference between these dependencies for the transparent prismatic sectors. It is clear
from figure 3 that the prismatic sector of KDP+A crystal contains much less “blocking” polyvalent
impurities than KDP+CSB crystal. As a result, the prism of KDP+A crystal becomes almost as
free from these impurities as it is in pure KDP crystal grown by the classical method. It means
that the molecules of organic dyes A being introduced into KDP, staining the pyramidal sectors
of the crystal and leaving prismatic sectors unstained, practically do not affect the degree of
defectiveness of a pyramid and are responsible for a substantial purification of the prismatic sector
from the blocking polyvalent ions and for the reappearance of the “plateau”, typical of the high
quality KDP crystals grown using the traditional method. This purification can be connected with
the formation of stable complexes of organic dye molecules with polyvalent cation background
impurities and neutralization of their effect upon the prismatic sectors.
Figure 4. Temperature dependence of the in-
verse dielectric constant of pyramidal sector of
KDP+A near TC .
Figure 5. Temperature dependence of the in-
verse dielectric constant of prismatic sector of
KDP+A near TC .
Measurements of dielectric constant in the vicinity of the transition point (TC = 121.8 K )
revealed two peculiarities of the doped samples. The first one is a small (near 0.1 K) hysteresis of
the transition point on cooling and heating which is typical for the first-order phase transition close
to the tricritical point. The second is the remarkable difference of dielectric constant on cooling
and heating in ferroelectric phase for the pigmented pyramidal sectors (figure 4). The latter effect
is not pronounced for the transparent (prismatic) sectors (figure 5). Moreover, in KDP+A crystal
the form of ε(T ) dependence near TC looks (for the prism sector) almost completely similar to the
one for the pure KDP crystal grown using the traditional method [13]. The small smearing of the
phase transition (which is more pronounced for KDP+CSB crystal) without a visible shift of the
transition temperature is evident for the stained parts of the crystal.
4. Thermal properties: pyramid-stained crystals
We have measured the specific heat C(T ) for the prism and pyramid of pure KDP, KDP+CSB
and KDP+A. It was found that far from TC, all experimental curves are practically identical within
an accuracy of measurements. In the region of phase transition (TC ± 0.3 K) the situation in pure
and doped crystals was revealed as quite different. The sharp decrease of maximum value of the
114
KDP crystals with the complex impurities
specific heat at TC and the change of the form of C(T ) dependencies were observed for the stained
pyramidal parts of KDP+CSB and KDP+A crystal (figure 6a); for the relatively pure transparent
prismatic sectors of KDP+CSB crystal the reproducible splitting of the specific heat anomaly was
detected (figure 6b).
Figure 6. Temperature dependence of specific heat near TC for the stained pyramidal parts of
KDP+CSB and KDP+A crystals (a); the same for the prismatic part of crystal KDP+CSB (b).
It is seen that the form of C(T ) dependencies in figure 6a looks like the one for pure KDP crys-
tal located in the external electric field [15,16] with the only difference that the maximum value
of the specific heat of pigmented parts of the crystals is not shifted to higher temperatures. This
phenomenon can be explained within the theory of the phase transitions in defected crystals pre-
dicted the displacement of the transition point to lower temperatures [17]. To analyse the reason of
splitting of the specific heat anomaly observed in relatively pure prismatic sector of KDP+CSB (fi-
gure 6b) we should take into account the fact that such a phenomenon was observed earlier for
some defected KDP crystals [18,19]. In our case we can assume that even in the transparent part
of the crystal there is some amount of the CSB dye molecules – polar defects – which are randomly
distributed in the crystal forming the inner biasing field. It was demonstrated by Duckek and Falk
in [20] that for the first-order ferroelectric phase transition which is close to a tricritical point,
the occurrence of metastable states is possible in an external electric field. That is the case when
Figure 7. Temperature dependence of polarization for KDP crystal in different external electric
field. Upper curves – for the stable states (E ↑↑ P ), lower – for the unstable states (E ↑↓ P ).
Ec – electrical “critical” field removing the jump of polarization at TC .
polarization of the ferroelectric is directed opposite to the field. For the inner biasing field created
by the defects themselves the situation is possible when one part of the crystal volume will be in
the stable state (polarization P+ is along the field) whereas the other part will be in metastable
115
B.Strukov, I.Shnaidshtein, S.Grabovsky
state (polarization P
−
is counter the field). This idea is supported by the fact that the spontaneous
polarization calculated from the specific heat data was found to be by 8–10% less in doped crystal
in comparison with the pure one.
Denoting the latter (relative) part as s, we shall have for the anomalous part of specific heat
for such a crystal as C = (1 − s)C(P+) + sC(P
−
). The part of P (T ) dependencies constructed
according to Duckek and Falk theory is presented in figure 7 with the Landau parameters taken
from [16]; the corresponding specific heat temperature dependence is shown in figure 6b as a solid
line (s = 0.04); the coincidence of the experimental points with the calculated curve is fairly good.
5. Dielectric properties: prism-stained crystals
It has been already pointed out that dyes can selectively penetrate into different sectors of
the crystal. This feature of dyes is probably connected with the stereochemical affinity of the
dye with the crystal lattice [11]. The nature of this affinity is not clear at present although some
assumption for the dyes with the relatively simple structure will be done in the next section. The
question is whether the properties of the doped KDP crystal with the stained prism are similar
to the above considered case of stained pyramid. In the only paper where the phase transition in
the prism-stained KDP crystal was studied (with hematein as a dopant) the authors revealed the
noticeable lowering of the transition point [10]; we have not detected this effect for the pyramid-
stained crystals. Dielectric data for two prism-stained crystal – KDP+PCR and KDP+XO were
obtained. The small size of the samples gave us no chance to measure specific heat of these crystals.
The structural formulas for the both molecules – Pento-Cloro-Ruthenate and Xelenol Orange are
presented in figure 1. As to PCR, the evident stereochemical affinity of the matrix and impurity
causes the joining of the molecules to prismatic sector; evidently, the anion [Ru2Cl10O]4− formed
in a solution penetrates as a whole into the growing crystal. The structure of the organic dye has
no visible features of affinity with the crystal lattice and this impurity is completely nonisomorphic
to the matrix; it is not clear at present why these molecules “choose” mainly prismatic sectors.
Figure 8. Temperature dependence of dielectric constant of KDP+PCR in the wide temperature
range (a) (1 – transparent pyramid, 2 – pigmented prism) and of the reciprocal dielectric constant
in the vicinity of TC (b)(1.2 – the same as in (a)).
The temperature dependence of dielectric constant of KDP+PCR crystal is shown in figure 8a.
It is evident that there is almost complete suppressing of the domain contribution into dielectric
constant of the stained prismatic sector, and ε(T ) anomaly has a symmetrical form unusual for KDP
crystals with the Curie–Weiss law being fulfilled for both phases. For the transparent pyramidal
sector ε(T ) dependence is qualitatively identical with the one for the pure KDP crystal showing
the typical “shoulder” in the polar phase. It is remarkable that the data in the very vicinity of
the transition point reveal the difference of transition temperatures for samples cut from different
sectors of the doped crystal (figure 8b): the maximum value of dielectric constant corresponds to
116
KDP crystals with the complex impurities
121.60 K for the transparent pyramidal sector and 121.25 K for the stained prisma. Therefore, our
data are in accordance with the results of [10] obtained for KDP crystals doped by hematein.
In the case of KDP+XO crystal, the results were less determined. The comparison of its prop-
erties with the properties of pure crystal shows that the impurity penetrates to both prismatic
and pyramidal sectors, though its concentration in the pyramid is much less than in the prism; the
shift of the transition point was not detected, but the suppressing of the domain contribution in
dielectric constant was found to be remarkable in the more intensively stained pyramidal sector.
6. The possible model of penetrating: Amaranth case
The problem of the large complex dye molecules penetrating into KDP structure was dis-
cussed in [11,12]. In accordance with the proposed model the stereochemical affinity is supposed
to be an important factor of the partially ordered disposition of the impurity molecules in the
crystal matrix. Thus, the end groups SO−
3 of the dye molecules can presumably occupy the po-
sitions of PO−
4 groups in KDP lattice. If one considers a dye molecule as a rigid complex, the
strong local mechanical deformation of crystal lattice can be proposed around this molecule.
Figure 9. Presumable scheme of the dispo-
sition of Amaranth molecule in KDP struc-
ture.
So far as we found no data on the interatomic dis-
tances for the dye molecule Amaranth possessing the
simplest structure, we used the quantum-chemical
set of program GAMESS [21] for the calculation of
the space geometry of this molecule exploiting the
principle of the minimum energy. The direct com-
parison of the parameters of the dye molecule with
the crystal structure of KDP crystal revealed the
following features. The most probable region of the
impurity molecule inclusion is the diagonal plane of
the elementary cell (figure 9). The mechanical strain
accompanying such a disposition can be considered
as the increasing of a1 parameter by 0.55 Å and si-
multaneous decreasing of a2 by 0.56 Å in the initial
nonstrained cell plus shear in the basic plane, de-
creasing the angle between a1 and a2 by 6% . It
means that the local strains in the region of the
molecule localization are similar to the strains of KDP lattice arising at the phase transition.
Of course, such speculations become very difficult for the dyes with the more intricate molecular
structure.
7. Conclusions
We have studied dielectric and thermal properties of KDP crystals doped with dye molecules
staining different sectors of growth of crystal matrix. The dielectric measurements revealed that the
dye molecules pigmenting the pyramidal sectors and leaving the prismatic ones transparent, only
slightly affect the domain contribution into dielectric constant of the polar phase and do not shift
the transition point; at the same time, they are responsible for cleaning the prismatic sectors from
polyvalent metal impurities. This causes a remarkable increase of dielectric constant of the prism
and the appearance of the “plateau” region which is typical of the high quality KDP crystals. On the
contrary, the complex impurities selectively entering the prismatic sector almost completely sup-
press the domain contribution into dielectric constant of this sector and slightly decrease the tran-
sition temperature, leaving the dielectric constant of the transparent pyramidal sector unchanged.
It is shown that the specific heat of the pure and doped KDP is different in the interval of about 1 K
near TC for the pyramid-stained crystals. The appearance of the biasing field directed counter the
spontaneous polarization was considered in interpreting the obtained specific heat temperature de-
pendencies. The presumable model of Amaranth dye molecule entering the KDP lattice is proposed.
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B.Strukov, I.Shnaidshtein, S.Grabovsky
8. Acknowledgements
Authors thank the RFBR for the financial support of this research (project 05-02-16873a),
N. Zaitseva and L. Carman for the samples of KDP+CSB and KDP+A crystals, B. Kahr for
the samples of KDP+PCR crystals and I. Pritula and Yu. Velikhov for the samples of KDP+XO
crystals. The discussions with L. Rashkocich are very much appreciated.
References
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Фазовi переходи в кристалах KDP з комплексними
органiчними та неорганiчними домiшками
Б.Струков, I.Шнадштейн, С.Грабовський
Московський державний унiверситет iм. Ломоносова, 119992 Москва, Росiя
Отримано 4 вересня 2006 р.
У цiй статтi ми представляємо результати вивчення дiелектричних та термiчних властивостей кри-
сталiв KDP, легованих рiзноманiтними комплексними органiчними та неорганiчними молекулами,
якi покривають рiзнi (пiрамiдальнi або призматичнi) дiлянки росту кристалу. Показано, що власти-
востi зафарбованих i прозорих частин кристалу у порiвняннi з вiдповiдними дiлянками номiнально
чистого кристалу є рiзними для кристалiв KDP, вирощених з використанням традицiйної (повiль-
ної) та швидкої технологiй вирощування. Представлено та проаналiзовано вiдмiннiсть доменного
вкладу у дiелектричну сталу полярної фази та характерний гiстерезис для чистих i зафарбованих
кристалiв, розташування температури переходу та форму аномалiї теплоємностi. Запропоновано
найбiльш правдоподiбну модель включення молекул комплексних домiшок у структуру KDP.
Ключовi слова: сегнетоелектрики, домiшки, дiелектична стала, молекули фарбника,
теплоємнiсть, вирощування кристалiв
PACS: 81.10.Aj, 61.72.Ww, 77.84.Fa, 77.80.Dj, 77.80.Bh
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