Original scientific paper
/midem
Journal of M
Informacije |
Journal of Microelectronics, Electronic Components and Materials Vol. 45, No. 4 (2015), 260 - 265
Specific heat capacity and thermal conductivity of the electrocaloric (1-x)Pb(Mg1/3Nb2/3)O—xPbTiO3 ceramics between room temperature and 300oC
Hana Uršič1'2, Marko Vrabelj1,2, Lovro Fulanovič12, Andraž Bradeško1,2, Silvo Drnovšek1, Barbara Malič12
1Jozef Stefan Institute, Electronic Ceramics Department, Ljubljana, Slovenia 2Jozef Stefan Postgraduate School, Ljubljana, Slovenia
Abstract: We report the specific heat capacity and thermal conductivity of electrocaloric (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (x = 0, 0.1, 0.3 and 0.35) ceramics between room temperature and 300 °C. The specific heat capacity for all ceramic samples is between 0.323 and 0.326 J/gK at 35 °C. For the samples with a high PbTiO3 content (x = 0.3 and 0.35), a pronounced anomaly is observed in the specific heat capacity versus temperature at 130 °C and 153 °C, indicating the phase transition from the polar to a non-polar phase. The thermal conductivity in this system significantly depends on the PbTiO3 content. The lowest thermal conductivity is obtained for Pb(Mg1/3Nb2/3)O3, and it increases with increasing PbTiO3 content in the whole temperature range. For example at 23 °C the values of thermal conductivity of Pb(Mg1/3Nb2/3)O3 and 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 are 1.25 W/mK and 1.43 W/mK, respectively.
Keywords: PMN-PT; thermal conductivity; specific heat capacity; relaxor-ferroelectric; electrocaloric
Specifična toplotna kapaciteta in toplotna prevodnost elektrokalorične keramike (1-x)Pb(Mg1/3Nb2/3)O—xPbTiO3 v temperaturnem območju od sobne temperature do 300°C
Izvleček: V članku poročamo o specifični toplotni kapaciteti in toplotni prevodnosti elektrokalorične keramike (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (x = 0, 0,1, 0,3 in 0,35) v temperaturnem območju od sobne temperature do 300 °C. Specifična toplotna kapaciteta vseh merjenih vzorcev se pri 35 °C giblje v intervalu med 0,323 in 0,326 J/gK. Ko vzorce segrevamo, pri vzorcih z večjim deležem PbTiO3 (x = 0,3 in 0,35) v meritvah toplotne kapacitete opazimo anomalijo, ki je značilna za premeno iz polarne v nepolarno fazo. Toplotna prevodnost trdne raztopine je izrazito odvisna od deleža PbTiO3. Pb(Mg1/3Nb2/3)O3 izkazuje manjšo toplotno prevodnost kot 0,65Pb(Mg1/3Nb2/3)O3-0,35PbTiO3 v celotnem temperaturnem območju. Na primer, pri temperaturi 23 °C je toplotna prevodnost Pb(Mg1/3Nb2/3)O3 enaka 1,25 W/mK, medtem, ko je toplotna prevodnost 0,65Pb(Mg1/3Nb2/3)O3-0,35PbTiO3 za 13 % višja.
Ključne besede: PMN-PT; toplotna prevodnost; specifična toplotna kapaciteta; relaksor-feroelektrik; elektrokalorik * Corresponding Author's e-mail: hana.ursic@ijs.si
1 Introduction
The relaxor-ferroelectric (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-100xPT) ceramics exhibit a high dielectric permittivity, polarization, electromechanical [1-4] and electrocaloric (EC) effects [5, 6] and can be used for different applications, such as piezoelectric sensors, actuators, transducers [7-10] and cooling devices of a
new generation [11, 12]. In our previous work we have shown that PMN-30PT [13] and PMN-10PT [14] bulk ceramics possess the EC temperature changes (DTEC) as high as 2.7 °C and 3.5 °C, respectively. These values are the highest reported for the lead-based ceramics [5, 6]. By using such ceramic PMN-PT elements in a cooling device with the efficient heat regeneration system, the
260
© MIDEM Society
M. Malajner et al; Informacije Midem, Vol. 45, No. 4 (2015), 237 - 248
temperature span between the hot and the cold sides of the regenerator can exceed the temperature change of a single PMN-PT ceramic plate by several times [11]. However, when designing an EC device not only the EC properties, but also the thermal properties of the EC materials may have a great impact on its efficiency. Heat diffuses out of an EC layer of the thickness d in the time tdiff ~ d2Cp/X, where Cp is the specific heat capacity and X is the thermal conductivity [15, 16]. Therefore for an efficient cooling device, the EC material should possess a low C to X ratio.
enized powder mixture was high-energy milled in a Retsch PM 400 planetary mill at 300 rpm for up to 140 h, and additionally milled in a Netzsch PE 075 / PR 01 at-tritor mill at 800 rpm for 4 h in isopropanol. The powder compacts were pressed uniaxially at 50 MPa and then isostatically at 300 MPa. The compacts were sintered in double alumina crucibles in the presence of the packing powder of the same composition at 1200 °C for 2 h with the heating and cooling rates 2 °C/min. Regarding the synthesis procedure of PMN-100xPT please see also [2, 13, 14, 17].
In the present study we report the specific heat capacity and thermal conductivity of the PMN-100xPT ceramics of different compositions, i.e., x = 0, 0.1, 0.3 and 0.35. These material compositions were intentionally selected due to their specific properties. The PMN-rich compositions are of interest because of their large room temperature EC effects [13, 17, 18]. Furthermore, it has been recently shown that for a highly-efficient device the PMN and PMN-10PT ceramic elements are preferable than the elements from the PT-rich compositions due to their slim polarization versus electric field hysteresis loops and consequent lower losses [19]. On the other hand the PMN-35PT composition is the morphotropic phase boundary (MPB) composition and possesses high piezoelectric [1-3] as well as EC properties [14, 19], which could be an added value in the development of multifunctional devices.
The Cp was mainly studied in PMN and PMN-PT single crystals [20-25]. Only the Cp of PMN ceramics can be found in the literature [26, 27]. The X of PMN and PMN-PT materials were previously studied mainly in the single-crystal form [20, 28-31] in the range between -271 °C and 117 °C. A few studies report the X of PMN ceramics, but only at very low temperatures (i.e., from -271 °C to -173 °C) [26, 32]. The temperature dependence of DTEC for PMN-PT exhibits the maximum value at the relaxor-to-ferroelectric phase-transition temperature [13, 14], which typically takes place in the middle of the low-temperature slope of the dielectric permittivity peak, i.e., below room temperature for PMN, and at ~160 °C for PMN-35PT. For designing cooling devices based on EC materials, the knowledge of the thermal properties of the PMN-PT ceramics is needed, especially at elevated temperatures.
2 Materials and methods
For the synthesis of the stoichiometric PMN-100xPT (x = 0, 0.1, 0.3 and 0.35) ceramic powder, PbO (99.9 %, Al-drich), MgO (99.9 % Alfa Aesar), Nb2O5 (99.9 %, Aldrich) and TiO2 (99.8 %, Alfa Aesar) were used. The homog-
The densities of the sintered pellets were measured with a gas-displacement density analyser (Micromeri-tics, AccuPyc III 1340 Pycnometer). The relative densities (RD) of the samples were 97.08 %, 95.52 %, 96.31 % and 97.59 % for the compositions with increasing PT content. For these calculations the theoretical density of PMN was used, i.e., 8.13 g/cm3 (JCPDS 81-0861). For the microstructural analysis with a field-emission scanning electron microscope FE-SEM (JEOL FEG-SEM JSM-7600) the samples were ground, polished and thermally etched. The FE-SEM images of the etched surfaces reveal homogeneous and uniform microstructures (Figure 1). For the stereological analyses more than 250 grains per sample were measured. The grain size (GS) is expressed as the Feret's diameter (Figure 1).
Figure 1: FE-SEM micrographs of PMN-100xPT (x = 0, 0.1, 0.3 and 0.35) ceramics.
The specific heat capacity versus temperature Cp(T) of the ceramic samples was determined from the differential scanning calorimetry curves measured using a differential scanning calorimeter DSC (Netzsch, DSC 204 F1). The samples of ~5 mm in diameter and the thickness of ~1 mm were put in Pt crucibles with lids, and heated in a calorimeter with a heating rate of 2 °C/ min from 35 °C to 300 °C. Each measurement was repeated two times. To determine the C of the samples,
261
A. R. Buzdar et al; Informacije Midem, Vol. 45, No. 4 (2015), 225 - 236
sapphire (Netzsch, diameter of 5.2 mm, thickness of 1 mm) was used as the standard material.
For the measurements of the thermal transport properties versus temperature, the 8 mm thick pellets with 18 mm in diameter were prepared. The measurements were performed by the transient plane source technique [33] using the HotDisk TPS 2500S equipment (Hot Disk AB, Gothenburg, Sweden). The HotDisk sensor (Mica, 3.2 mm diameter, C5465) was placed between two ceramic pellets. The basic principle of the system is to supply the constant power to the sample via a Hot Disk sensor. The sensor is used as the heat source and the temperature monitor. The material was heated at 100 mW for 10 s. The length of the heating pulse was chosen short enough so that the sensor could be considered in contact with an infinite solid throughout the recording. In this way the thermal properties of the studied material could be determined by measuring the temperature increase of the sensor in a short period of time [34, 35]. The measurements at elevated temperatures (from 50 °C to 300 °C) were performed in a tube furnace (Entech) in nitrogen atmosphere to prevent the oxidation of the sensor. The step and the stabilization time of the measurements were 10 °C and 15 min, respectively. The step of 2 °C was used for the measurements performed in the range close to the phase transition temperature from polar to non-polar phases for PMN-30PT and PMN-35PT samples. At each temperature 5 measurements were performed. The waiting time between each measurement was long enough that the sample temperature reached the equilibrium with the furnace temperature (5 min). The room temperature measurements (i.e. 23 °C) were performed in air. In order to compare the thermal conductivity of ceramic samples with different chemical composition, i.e., PMN-100xPT (x = 0, 0.1, 0.3 and 0.35), the thermal conductivities were normalized to the sample density using the equation:
k =
K -Kir(1 'P) P
(1)
where Xm is the measured thermal conductivity of the sample, Xair is the thermal conductivity of the air, which is equal to 0.026 W/mK [36] and p is the RD of the sample.
3 Results and discussion
The specific heat capacity, Cp, versus temperature of PMN-100xPT (x = 0, 0.1, 0.3 and 0.35) ceramic samples is shown in Figure 2, and the values of Cp at selected temperatures are collected in Table 1. At 35 °C the C
is between 0.323 and 0.326 J/gK for all samples. These values are in a good agreement with previously published data for PMN-29PT single crystals [24]. The Cp of PMN and PMN-10PT increases continuously with increasing temperature. In PMN such slow increase of Cp is observed up to ~220 °C, and at higher temperatures it remains almost constant. In PMN-10PT, the plateau is reached at a lower temperature, at ~120 °C (Table 1).
	0.42-
	0.40-
	
	
-1	0.38-
a	
u	
	0.36-
	0.34-
	0.32-
PMN-35PT	
PMN-30PTAJ	
J^^PMI^OPT "^jjMlIM	
	"PMN
50
100
150 T (X)
200
250
T
300
Figure 2: The Cp(T) of PMN-100xPT (x = 0, 0.1, 0.3 and 0.35) ceramics.
Table 1: Selected Cp values of PMN-100xPT samples (from Figure 2).
Cp (J/gK)				
T	PMN	PMN-10PT	PMN-30PT	PMN-35PT
35 °C	0.326	0.325	0.326	0.323
50 °C	0.330	0.335	0.336	0.332
100 °C	0.340	0.347	0.355	0.350
200 °C	0.345	0.349	0.363	0.362
300 °C	0.346	0.350	0.357	0.353
In PT-rich compositions the Cp(T) behaviour is different;
clear anomalies in C are observed at 130 °C and 153 °C
p
related to the phase transitions from monoclinic and tetragonal phases to the high temperature cubic phase for PMN-30PT and PMN-35PT, respectively. These temperatures are in a good agreement with the published temperatures of dielectric permittivity anomalies; for PMN-30PT at ~130 °C (at 0.4 kHz) [14] and for PMN-35PT at ~160 °C (at 1 kHz) [1]. The phase transition anomaly observed in PMN-35PT is much more pronounced (DC = 0.062 J/gK) in comparison to the one observed in PMN-30PT (DCp= 0.008 J/gK). No anomalies have been detected in PMN and PMN-10PT samples within our temperature measurement range. Namely, for PMN and PMN-10PT ceramics the dielectric anomalies were reported at ~-15 °C [37] and ~40 °C [13, 37] (at 1 kHz), respectively, which is below or close to the lower limit of our measurement range.
262
A. R. Buzdar et al; Informacije Midem, Vol. 45, No. 4 (2015), 225 - 236
The temperature dependence of thermal conductivity, X, of PMN-100xPT ceramic samples is shown in Figure 3 and the X values at selected temperatures are given in Table 2. At 23 °C the X values of Pb(Mg1/3Nb2/3)O3 and 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 are 1.25 W/mK and 1.43 W/mK, respectively. The X increases with increasing temperature for all samples until approximately 250 °C, while above this temperature it is approximately constant. Such non-linear behaviour of the X(T) has been also observed in PMN-PT single crystals [20]. An interesting observation deduced from Figure 3 is that X significantly increases with increasing PT content in the whole temperature range which is in agreement with [31], where PMN single crystals possess lower X in comparison to PT single crystals in the whole measurement range, i.e., from -271 °C to 117 °C. Thermal conductivity measurements of BaTiO3 and KNbO3 single crystals revealed anomalies in X(T at the phase transition temperatures [31]. In our study, no such anomalies were observed for PMN-30PT and PMN-35PT at our measurement conditions, i.e., with the step of 2 oC in the temperature intervals close to the respective phase transition temperature from ferroelectric to high-temperature cubic phase, see the insets in Figure 3.
Figure 3: The U(T of PMN-100xPT (x = 0, 0.1, 0.3 and 0.35) ceramics. Insets: The U(T) of PMN-30PT (below) and PMN-35PT (above) measured in the range close to the phase transition temperature from ferroelectric to the high-temperature cubic phase.
Table 2: Selected values of U from Figure 3.
A (W/mK)				
T	PMN	PMN-10PT	PMN-30PT	PMN-35PT
23 °C	1.25	1.27	1.38	1.43
50 °C	1.30	1.32	1.41	1.45
100 °C	1.36	1.39	1.47	1.53
200 °C	1.43	1.46	1.59	1.64
300 °C	1.47	1.51	1.66	1.71
As previously mentioned for the efficient cooling device, the Cp to X ratio of EC material should be as low as possible. The values of the Cp/X ratio of PMN-100xPT ceramic samples (x = 0, 0.1, 0.3 and 0.35) are shown in Figure 4. In the whole measurement range the lowest Cp/X ratio is obtained for PMN-35PT ceramics and the highest ones are obtained for PMN and PMN-10PT ceramics. For example, at 50 °C the Cp/X ratio of PMN-35PT is for 10 % lower than the one of PMN-10PT and PMN samples. Note also that the anomaly in the C /X(T) of PMN-30PT and PMN-35PT appears at 130 °C and 153 °C, respectively, and it is the result of the pronounced anomaly obtained in the Cp(T) measurement (see Figure 2).
Figure 4: The Cp/X(T) of PMN-100xPT (x = 0, 0.1, 0.3 and 0.35) ceramics.
4 Summary and conclusions
In the present work, we examined the thermal properties of PMN-PT, which is one of the most promising EC materials compositions. We studied four different compositions; from relaxor PMN to the MPB composition PMN-35PT. The measurements of specific heat capacity versus temperature Cp(T) vary for different PMN-PT compositions. At 35 °C the Cp is between 0.323 and 0.326 J/gK. With increasing temperature, the Cp increases continuously untill it reaches the plateau value in PMN and PMN-10PT. No anomalies are observed in the whole measured temperature range. In PT-rich compositions the Cp(T) dependence is different; pronounced anomalies are observed at 130 °C and 153 °C for PMN-30PT and PMN-35PT, respectively. The temperatures at which the anomalies occur correspond to the previously published phase transition temperatures from polar to high-temperature non-polar phases obtained from dielectric spectroscopy data. The heat capacity anom-
263
A. R. Buzdar et al; Informacije Midem, Vol. 45, No. 4 (2015), 225 - 236
aly observed in PMN-35PT is much more pronounced (AC = 0.062 J/gK) in comparison to the one observed in PmN-30PT (AC = 0.008 J/gK).
The thermal conductivity X of PMN at 23 oC is 1.25 W/ mK, while the one of PMN-35PT is about 13 % larger. Such increase of X with increasing PT content in the PMN-100xPT materials persists within the whole measurement temperature range.
To conclude, for an efficient cooling element the EC material should possess a low Cp/X ratio. PMN-35PT ceramics possess the lowest CJX ratio in the whole measurement range is spite of the anomaly at ~153 °C. On the other hand, the PMN and PMN-10PT materials possess a higher CJX ratio, but no pronounced anomaly in CJX is detected in this measurement range. The answer to the question: "Which composition of PMN-PT material is more appropriate for use in efficient EC cooling device of new generation?" is not trivial. From the thermal point of view, the more appropriate compositions are the ones with higher amounts of PT (i.e., PMN-30PT and PMN-35PT), but on the other hand these compositions possess high piezoelectric coefficients and well defined ferroelectric hysteresis loops, which could be a drawback for some specific electrocaloric applications.
5 Acknowledgements
The authors thank the Slovenian Research Agency for financial support in the frame of the projects L2-6768, doctoral projects PR-06166, PR-06804, PR-05025 and program P2-0105. Centre of Excellence NAMASTE is acknowledged for access to the HotDisk TPS 2500S equipment.
6 References
1.	J. Kelly, M. Leonard, C. Tantigate, A. Safari: Effect of composition on the electromechanical properties of (1-x)Pb(Mg1/3 Nb2/3)O3- xPbTiO3 ceramics, J. Am. Ceram. Soc. 1997, 80, 957.
2.	H. Uršič, J. Tellier, M. Hrovat, J. Holc, S. Drnovšek, V. Bobnar, M. Alguero, M. Kosec: The Effect of Poling on the Properties of 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 Ceramics, Jpn. J. Appl. Phys. 2011, 50, 035801.
3.	T. Y. Koo, S. W. Cheong: Dielectric and piezoelectric enhancement due to 90° domain rotation in the tetragonal phase of Pb(Mg1/3Nb2/3)O3-PbTiO3, Appl. Phys. Lett. 2002, 80, 4205.
4.	H. Uršič, M. Škarabot, M. Hrovat, J. Holc, M. Skalar, V. Bobnar, M. Kosec, I. Muševič:
The electrostrictive effect in ferroelectric 0.65Pb(Mg1/3Nb2/3)O3 -0.35PbTiO3 thick films, J. Appl. Phys., 2008,103, 12410 1.
5.	M. Valant: Electrocaloric materials for future solidstate refrigeration technologies, Prog. Mater. Sci., 2012, 57, 980.
6.	X. Moya, S. Kar-Narayan, N. D. Mathur: Caloric materials near ferroic phase transitions, Nat. Mater. 2014, 13, 439.
7.	H. Uršič, F. Levassort, J. Holc, M. Lethiecq, M. Kosec: 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 Thick Films for High-Frequency Piezoelectric Transducer Applications, Jpn. J. Appl. Phys. 2013, 52, 055502.
8.	F. Levassort, A. C. Hladky-Hennion, H. Le Khanh, P. Tran-Huu-Hue, M. Lethiecq, M. Pham Thi: 0-3 and 1-3 piezocomposites based on single crystal PMN-PT for transducer applications, Advances in Applied Ceramics, 2010, 109, 162.
9.	J. F. Tressler, S. Alkoy, R. E. Newnham: Piezoelectric sensors and sensor materials, J. Electroceram., 1998, 2, 257.
10.	H. Uršič, M. Hrovat, J. Holc, S. M. Zarnik, S. Drnovšek, S. Maček: Sensors Actuat. B, 2008, 133, 699.
11.	U. Plaznik, A. Kitanovski, B. Rožič, B. Malič, H. Uršič, S. Drnovšek, J. Cilenšek, M. Vrabelj, A. Poredoš, Z. Kutnjak: Bulk relaxor ferroelectric ceramics as a working body for an electrocaloric cooling device, Appl. Phys. Lett. 2015, 106, 043903.
12.	X. Moya, E. Defay, V. Heine, N. D. Mathur: Too cool to work, Nat. Phys., 2015, 11, 202.
13.	M. Vrabelj, H. Uršič, Z. Kutnjak, B. Rožič, S. Drnovšek, A. Benčan, V. Bobnar, L. Fulanovic, B. Malič: Large electrocaloric effect in grain-size-engineered 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3, J. Eur. Ceram. Soc., 2016, 36, 75.
14.	B. Rožič, M. Kosec, H. Uršič, J. Holc, B. Malič, Q.M. Zhang, R. Blinc, R. Pirc, Z. Kutnjak: Influence of the critical point on the electrocaloric response ofrelaxor ferroelectrics, J. Appl. Phys. 2011, 110, 064118.
15.	R. I. Epstein and K. J. Malloy: Electrocaloric devices based on thin-film heat switches, J. Appl. Phys. 2009, 106, 064509.
16.	S. Karmanenko, A. Semenov, A. Dedyk, A. Eskov, A. Ivanov, P. Beliavskiy, Y. Pavlova, A. Nikitin, I. Star-kov, A. Starkov, O. Pakhomov: New Approaches to Electrocaloric-Based Multilayer Cooling (Eds: T. Correia, Q. Zhang), Springer-Verlag, Berlin Heidelberg, Germany, 2014, pp. 186.
17.	B. Rožič, B. Malič, H. Uršič, J. Holc, M. Kosec & Z. Kutnjak: Direct Measurements of the Electrocaloric Effect in Bulk PbMg1/3Nb2/3O3 (PMN) Ceramics, Ferroelectrics, 2011, 421, 103.
18.	J. Perantie, H. N. Tailor, J. Hagberg, H. Jantunen, Z.-G. Ye, Electrocaloric properties in relaxor fer-
264
H. Ursic et al; Informacije Midem, Vol. 45, No. 4 (2015), 260 - 265
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
roelectric (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 system, J.Appl. Phys. 2013, 114, 174105. U. Plaznik, M. Vrabelj, Z. Kutnajk, B. Malic, A. Poredos, A. Kitanovski: Electrocaloric cooling: The importance of electric-energy recovery and heat regeneration, Europhysics Letters, 2015, 111, 57009.
M. Tachibana, E. Takayama-Muromachi: Thermal conductivity and heat capacity of the relaxor ferroelectric [PbMg^Nb^O^JPbTiOJ*, Phys. Rev. B 2009, 79, 100104.	*
Z. Kutnjak: Heat capacity response of relaxor fer-roelectrics near the morphotropic phase boundary, Ferroelectrics, 2008, 369, 198. N. Novak, G. Cordoyiannis, Z. Kutnjak, Dielectric and heat capacity study of (PtyMg^Nb^O^^-(PbTiO3)026 ferroelectric relaxor near the cubic-tetragonal-rhombohedral triple point, Ferroelectrics, 2012, 428, 43.
Z. Kutnjak, J. Petzelt, R. Blinc, The giant electromechanical response in ferroelectric relaxors as a critical phenomenon, Nature, 2006, 441, 956. Y. Tang, X. Zhao, X. Feng, W. Jin, H. Luo, Pyroelectric properties of [111]-oriented Pb(Mg1/3Nb2/3)O3-Pb-TiO3 crystals, Appl. Phys. Lett., 2005, 86, 08529(31.
A.	Fouskova, V. Kohl, N. N. Krainik, I. E. Mylnikova: Specific heat of PbMg1/3Nb2/3O3, Ferroelectrics, 1981, 34, 119.
D. A. Ackerman, D. Moy, R. C. Potter, A. C. Anderson, W.N. Lawless: Glassy behavior of crystalline solids at low temperatures, Phys. Rev. B 1981, 23, 3886.
M. V. Gorev, I. N. Flerov, V. S. Bondarev, Ph. Sciau: Heat Capacity Study of Relaxor PbMg1/3Nb2/3O3 in a Wide Temperature Range, Journal of Experimental and Theoretical Physics, 2003, 96, 531. W. Hassled, E. Hegenbarth: Glasslike behaviour of thermal conductivity at ferroelectric single crystals of relaxor type, Ferroelectrics Letters, 1985, 4, 117-121.
D.M. Zhu, P. D. Han: Thermal conductivity and electromechanical property of single-crystal lead magnesium niobate titanate; Appl. Phys. Lett., 1999, 75, 3868.
J. J. De Yoreo, R. O. Pohl, G. Burns: Low-temperature thermal properties of ferroelectrics, Phys. Rev.
B,	1985, 32, 5780.
M. Tachibana, T. Kolodiazhnyi, E. Takayama-Muromachi: Thermal conductivity of perovskite ferroelectrics, Appl. Phys. Lett. 2008, 93, 092902. M. Fahland, E. Hegenbarth: Thermal conductivity of Pb(Mg1/3Nb2/3)O3 under the influence of high electric field, Ferroelectric Letters, 1993, 15, 89. S. E. Gustafsson: Transient plane source technique for thermal conductivity and thermal diffusivity
34.
35.
36.
37.
measurements of solid materials, Rev. Sci. Instrum. 1991, 797, 797.
Y. He: Rapid thermal conductivity measurement with a hot disk sensor, Part 1 and 2, Thermochimi-ca Acta, 2005, 436, 122.
B. Bertoncelj, K. Vojisavljevic, M. Vrabelj, B. Malic: Thermal properties of polymer-matrix composites reinforced with E-glass fibers, Informacije MIDEM, Journal of Microelectronics, Electronic Components and Materials, 2015, 45, 216. D. R. Lide: Handbook of chemistry and phyiscs, CRC Press LLC, 84 edition, 2003-2004, pp. 1161. S. L. Swartz, T.R. Shrout, W.A. Schulze, L.E. Cross, Dielectric properties oflead-magnesium niobate ceramics, J. Am. Ceram. Soc., 1984, 87, 311.
Arrived: 03. 12. 2015 Accepted: 02. 01. 2016
265