Dielectric relaxation in NaNbO₃ single crystal
Dielectric permittivity studies of reduced samples of NaNbO₃ single crystal in the range of temperatures 30–500 °C and frequency 20 Hz-1 MHz are reported. In this temperature range a relaxation process is observed in the frequency range of about 100 kHz. This is an additional process to the earlier...
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| Опубліковано в: : | Condensed Matter Physics |
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| Дата: | 1999 |
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Інститут фізики конденсованих систем НАН України
1999
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| Цитувати: | Dielectric relaxation in NaNbO₃ single crystal / K. Konieczny // Condensed Matter Physics. — 1999. — Т. 2, № 4(20). — С. 655-660. — Бібліогр.: 8 назв. — англ. |
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Konieczny, K. 2017-06-13T12:38:44Z 2017-06-13T12:38:44Z 1999 Dielectric relaxation in NaNbO₃ single crystal / K. Konieczny // Condensed Matter Physics. — 1999. — Т. 2, № 4(20). — С. 655-660. — Бібліогр.: 8 назв. — англ. 1607-324X DOI:10.5488/CMP.2.4.655 PACS: 77.22.Ch, 77.22.Gm https://nasplib.isofts.kiev.ua/handle/123456789/121010 Dielectric permittivity studies of reduced samples of NaNbO₃ single crystal in the range of temperatures 30–500 °C and frequency 20 Hz-1 MHz are reported. In this temperature range a relaxation process is observed in the frequency range of about 100 kHz. This is an additional process to the earlier reported one [7]. The obtained data were fitted to Cole-Cole formula. The dispersion step ∆ǫ (the maximum value of ∆ǫ =1000) is temperature dependent. The mean relaxation time τ does not obey the Arrhenius law above TC. The occurrence of this relaxation process may be connected with oxygen vacancies. Досліджено діелектричну сприйнятливість зразків монокристалу NaNbO₃ в діапазонах температур 30–500 °C і частот 20 Гц–1 МГц. У цьому температурному проміжку в частотній області поблизу 100 кГц спостерігається релаксаційний процес, що є доповнювальним до виявленого раніше процесу [7]. Отримані дані апроксимуються за формулою Коул-Коула. Значення дисперсії ∆ε (максимальне значення ∆ε = 1000) залежить від температури. Закон Арреніуса не виконується для середнього часу релаксації τ вище TC. Поява цього релаксаційного процесу може пов’язуватися з кисневими вакансіями. en Інститут фізики конденсованих систем НАН України Condensed Matter Physics Dielectric relaxation in NaNbO₃ single crystal Діелектрична релаксація в монокристалі NaNbO₃ Article published earlier |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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DSpace DC |
| title |
Dielectric relaxation in NaNbO₃ single crystal |
| spellingShingle |
Dielectric relaxation in NaNbO₃ single crystal Konieczny, K. |
| title_short |
Dielectric relaxation in NaNbO₃ single crystal |
| title_full |
Dielectric relaxation in NaNbO₃ single crystal |
| title_fullStr |
Dielectric relaxation in NaNbO₃ single crystal |
| title_full_unstemmed |
Dielectric relaxation in NaNbO₃ single crystal |
| title_sort |
dielectric relaxation in nanbo₃ single crystal |
| author |
Konieczny, K. |
| author_facet |
Konieczny, K. |
| publishDate |
1999 |
| language |
English |
| container_title |
Condensed Matter Physics |
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Інститут фізики конденсованих систем НАН України |
| format |
Article |
| title_alt |
Діелектрична релаксація в монокристалі NaNbO₃ |
| description |
Dielectric permittivity studies of reduced samples of NaNbO₃ single crystal in the range of temperatures 30–500 °C and frequency 20 Hz-1 MHz are reported. In this temperature range a relaxation process is observed in the frequency range of about 100 kHz. This is an additional process to the earlier reported one [7]. The obtained data were fitted to Cole-Cole formula. The dispersion step ∆ǫ (the maximum value of ∆ǫ =1000) is temperature dependent. The mean relaxation time τ does not obey the Arrhenius law above TC. The occurrence of this relaxation process may be connected with oxygen vacancies.
Досліджено діелектричну сприйнятливість зразків монокристалу
NaNbO₃ в діапазонах температур 30–500 °C і частот 20 Гц–1 МГц. У
цьому температурному проміжку в частотній області поблизу 100 кГц
спостерігається релаксаційний процес, що є доповнювальним до виявленого раніше процесу [7]. Отримані дані апроксимуються за формулою Коул-Коула. Значення дисперсії ∆ε (максимальне значення
∆ε = 1000) залежить від температури. Закон Арреніуса не виконується для середнього часу релаксації τ вище TC. Поява цього релаксаційного процесу може пов’язуватися з кисневими вакансіями.
|
| issn |
1607-324X |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/121010 |
| citation_txt |
Dielectric relaxation in NaNbO₃ single crystal / K. Konieczny // Condensed Matter Physics. — 1999. — Т. 2, № 4(20). — С. 655-660. — Бібліогр.: 8 назв. — англ. |
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AT koniecznyk dielectricrelaxationinnanbo3singlecrystal AT koniecznyk díelektričnarelaksacíâvmonokristalínanbo3 |
| first_indexed |
2025-11-25T22:33:24Z |
| last_indexed |
2025-11-25T22:33:24Z |
| _version_ |
1850566859871485952 |
| fulltext |
Condensed Matter Physics, 1999, Vol. 2, No. 4(20), pp. 655–660
Dielectric relaxation in NaNbO3 single
crystal
K.Konieczny
Institute of Physics and Computer Science, Pedagogical University,
2 Podchora̧żych Str., 30-084 Kraków, Poland
Received August 31, 1998, in final form December 15, 1999
Dielectric permittivity studies of reduced samples of NaNbO3 single crystal
in the range of temperatures 30–500 ◦C and frequency 20 Hz-1 MHz are
reported. In this temperature range a relaxation process is observed in
the frequency range of about 100 kHz. This is an additional process to the
earlier reported one [7]. The obtained data were fitted to Cole-Cole formula.
The dispersion step ∆ǫ (the maximum value of ∆ǫ =1000) is temperature
dependent. The mean relaxation time τ does not obey the Arrhenius law
above TC. The occurrence of this relaxation process may be connected
with oxygen vacancies.
Key words: NaNbO3, single crystal, reduced sample, dielectric relaxation,
oxygen vacancies
PACS: 77.22.Ch, 77.22.Gm
1. Introduction
The sodium niobate is a typical antiferroelectric with the perovskite structure.
In the temperature range from –200 ◦C to 650 ◦C its structural, dielectric and optic
properties are being changed in the six phase transitions. All these transitions are
connected with the oxygen octahedrons tilts and, in addition, the off-centre dis-
placement of the Nb ion takes place in the first three cases (–200 ◦C, 360 ◦C and
480 ◦C). The phase transition, at the temperature 360 ◦C, from antiferroelectric
phase with orthorhombic structure (Pbma) to the antiferroelectric orthorhombic
structure (Pnmm) is accompanied by the maximum change of dielectric permittiv-
ity [1-6]. The results of the investigations carried out for NaNbO3 single crystal in
the temperature range 30–500 ◦C and for frequencies 20 Hz-1 MHz have revealed the
low-frequency relaxation processes [7]. The mean relaxation times in these processes
obeyed the Arrhenius law in the vicinity of TC and the dispersion step ∆ǫ was de-
pendent on temperature. Both relaxation parameters ∆ǫ and τ revealed the distinct
discontinuity at the temperature TC. The arising of low-frequency relaxation has
c© K.Konieczny 655
K.Konieczny
10 100 1000 10000 100000 1000000
0
500
1000
1500
2000
2500
3000
3500 400oC, 673K
390oC, 663K
380oC, 653K
370oC, 643K
360oC, 633K
350oC, 623K
340oC, 613K
320oC, 593K
300oC, 573K
ε'
f(Hz)
10 100 1000 10000 100000 1000000
100
1000
10000
100000
1000000
f(Hz)
ε"
400oC, 673K
390oC, 663K
380oC, 653K
370oC, 643K
360oC, 633K
350oC, 623K
340oC, 613K
320oC, 593K
300oC, 573K
Figure 1. The frequency dependence of real ǫ′ and imaginary ǫ
′′ part of electric
permittivity.
656
Dielectric relaxation in NaNbO3
Figure 2. The example of fitting for 360 ◦C.
been connected with the disorder occurring in the crystalline structure already at
high temperatures, which can lead to the arising of local dipoles (polar regions).
These dipoles can be responsible for relaxation processes. In order to verify this
hypothesis, additional dielectric investigations of single crystals have been carried
out for reduced samples.
2. Experimental
The measurements were performed for a single crystal obtained by means of
the “flux” method (the crystal used in the investigations described in the paper
[8] was obtained using the same method). The crystal used in the measurements
was annealed at the temperature of about 550 ◦C during three hours in the vacuum
chamber (0.01 hPa) and then cooled (in vacuum) to the room temperature [8]. After
depositing the silver electrodes they were placed in the thermostat. The temperature
measurements were performed by means of a chromel-alumel thermocouple with the
accuracy equal to 0.1 ◦C. The capacity and dielectric loss measurements were carried
out using the HP 4284A LCR meter. The frequency of the measuring field was
20 Hz up to 1 MHz. Measurements were performed in regular steps of temperature
(each 10 ◦C) at a constant rate of temperature changes and at a constant time of
stabilisation.
657
K.Konieczny
200 250 300 350 400 450
0
200
400
600
800
1000
T
c
∆ε
T(
o
C)
0,0014 0,0016 0,0018 0,0020 0,0022
-14,0
-13,5
-13,0
-12,5
-12,0
-11,5
-11,0
-10,5
T
c
ln
τ
1/T(1/K)
Figure 3. The temperature depen-
dence of dispersion step ∆ǫ for B re-
laxation.
Figure 4. Arrhenius plot of the mean
relaxation time τ for B relaxation.
3. Results
Two relaxation processes were obtained. Except the weak relaxation process be-
low 10 kHz (the same as in the paper [7]) we can see the strong additional relaxation
arising below 100 kHz (figure 1). This relaxation shifts itself to lower frequencies,
when the temperature decreases. The results were fitted to the Cole-Cole model:
ǫ∗ = ǫ∞ +
ǫs − ǫ∞
1 + (iωτ)1−α
,
where ǫs is the static permittivity at low frequency, ǫ∞ is the permittivity measured
above the dispersion region, τ is the mean relaxation time, ω is the angular frequency
and α determines the distribution of relaxation times and has got values between 0
and 1. The increase of ǫ′′ towards low frequencies is associated with d.c. conductivity
represented by σC and giving a contribution to ǫ∗ in the form:
ǫ∗ = ǫ′ + i
(
ǫ′′p +
σC
ωǫ0
)
σC = exp
(
−
W
kT
)
.
The example of such a fitting for the temperature 360 ◦C is shown in figure 2. From
this figure we can distinguish two broad ǫ′′(f) contributions – A (the same as in the
paper [7]) and the additional one – B. The parameters of this relaxation are: A –
658
Dielectric relaxation in NaNbO3
∆ǫ=389, τ = 6.049 ·10−6, and B – ∆ǫ = 550, τ = 1.042 ·10−5 for temperature 360 ◦C
(above TC). The temperature dependence of dispersion step ∆ǫ for B-relaxation is
presented in figure 3. In the temperature range up to TC ∆ǫ ≈ const, however above
the temperature TC dispersion step ∆ǫ increases. The relaxation time in this process
does not obey the Arrhenius law above the temperature TC (figure 4).
4. Conclusions
It is well known, that the oxygen vacancies can be produced during the crystal
growth. Moreover these vacancies can be also produced by annealing the sample
in several oxygen atmospheres [8]. In the present paper the increase of the oxygen
vacancy concentration was produced by annealing the sample in a lower air pressure
atmosphere. The arising of the oxygen vacancies can be equivalent to the creation
of the local dipoles. The behaviour of these local dipoles in a.c. electric field leads
to the arising of an additional relaxation process in the NaNbO3 in the frequency
range of about 100 kHz (curve B in figure 2). This relaxation clearly evolves with
temperature (with decreasing of temperature it moves towards lower frequencies).
The studies of forming the vacancies and their effect on the behaviour of NaNbO3
requires additional investigations which are now in progress.
References
1. Cross L.E., Nicholson B.J. The optical and electrical properties of single crystals of
sodium niobate. // Phil. Mag., 1955, vol. 46, p. 453–466.
2. Ahtee M., Glazer A.M., Megaw H.D. The structures of sodium niobate between 480
and 575 ◦C, and their relevance to soft-phonon modes. // Phil. Mag., 1972, vol. 26,
No. 4, p. 995–1014.
3. Lefkowitz I., Lukaszewicz K., Megaw H.D. The high-temperature phase of sodium nio-
bate and the nature of transitions in pseudosymmetric structure. // Acta Cryst., 1966,
vol. 20, p. 670–683.
4. Ishida K., Honjo G. Soft modes and superlattice structure in NaNbO3. // J. Phys. Soc.
Japan, 1973, vol. 34, No. 5, p. 1279–1288.
5. Glaser A.M., Megaw H.D. Studies of the parameters and domains in the phase transition
of NaNbO3. // Acta Cryst., 1973, vol. A29, p. 489–495.
6. Kus Cz. Dielectric and Semiconductive Properties of NaNbO3. Kraków, WSP, 1991 (in
Polish).
7. Konieczny K., Kajtoch Cz. Low-frequency dielectric dispersion in NaNbO3 single crys-
tals. // Ferroelectrics, 1998, vol. 215, p.65–73.
8. Molak A. The influence of reduction in valency of Nb ions on the antiferroelectric phase
transition in NaNbO3. // Solid State Comm., 1987, vol. 62, No. 6, p. 413–417.
659
K.Konieczny
Діелектрична релаксація в монокристалі NaNbO3
К.Конєчни
Інститут фізики та обчислювальної техніки,
Педагогічний університет,
Польща, 30-084 Краків, вул. Подхоронжих, 1
Отримано 31 серпня 1998 р., в остаточному вигляді –
15 грудня 1999 р.
Досліджено діелектричну сприйнятливість зразків монокристалу
NaNbO3 в діапазонах температур 30–500 ◦C і частот 20 Гц–1 МГц. У
цьому температурному проміжку в частотній області поблизу 100 кГц
спостерігається релаксаційний процес, що є доповнювальним до ви-
явленого раніше процесу [7]. Отримані дані апроксимуються за фор-
мулою Коул-Коула. Значення дисперсії ∆ε (максимальне значення
∆ε = 1000) залежить від температури. Закон Арреніуса не виконуєть-
ся для середнього часу релаксації τ вище TC. Поява цього релак-
саційного процесу може пов’язуватися з кисневими вакансіями.
Ключові слова: NaNbO3, монокристал, діелектрична релаксація,
кисневі вакансії
PACS: 77.22.Ch, 77.22.Gm
660
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