The thermophysical properties of the ferroelectric PbFe 0.5 Nb 0.5 O 3 in the temperature range 300-800 K are studied. Anomalies in the heat capacity and thermal diffusion are found in the region of the diffuse ferroelectric transition T c ~380 K, the Burns temperature T d ~670 K, and the intermediate temperature T^*~470 K. The dominant phonon heat transfer mechanisms in a ferroelectric with a nanopolar structure. Keywords: heat capacity, thermal diffusion, thermal conductivity, ferroelectric, phase transitions, relaxor.

The thermophysical properties of the ferroelectric PbFe0.5Nb0.5O3 in the temperature range 300–800 K are studied. Anomalies in the heat capacity and thermal diffusion are found in the region of the diffuse ferroelectric transition Tc~380 K, the Burns temperature Td~670 K, and the intermediate temperature T^*~470 K. The dominant phonon heat transfer mechanisms in a ferroelectric with a nanopolar structure.

We studied the thermophysical and electrical properties of thermally expanded graphite in the temperature range of 300 to 800 K and found that the phonon contribution to heat transfer processes is dominant in this material. The temperature dependence of the mean free path of phonons is determined. The temperature dependences of the specific heat C p , thermal conductivity, and electrical conductivity revealed weak anomalies in the temperature range of 550 to 600 K. The thermal conductivity in thermally expanded graphite is two orders of magnitude lower than in ordinary graphite and three orders of magnitude lower than in graphene and carbon nanotubes.

Investigations of the heat capacity, thermal diffusivity, and thermal conductivity of multiferroics Bi1-xTmxFeO3 (x = 0, 0.05, 0.10, 0.20) have been carried out in the high temperature range of 300-1200 K. and thermal conductivity in the region of phase transitions. The temperature dependences of the specific heat for compositions with x = 0.10 and 0.20 exhibit an additional anomaly characteristic of the phase transition at T = 580 K. The dominant mechanisms of phonon heat transfer in the region of ferroelectric and antiferromagnetic phase transitions are considered. The temperature dependence of the average phonon mean free path is determined.

Investigations of the heat capacity, thermal diffusivity, and thermal conductivity of multiferroics Bi1-xTmxFeO3 (x=0, 0.05, 0.10, 0.20) have been carried out in the high temperature range of 300-1200 K. and thermal conductivity in the region of phase transitions. The temperature dependences of the specific heat for compositions with x=0.10 and 0.20 exhibit an additional anomaly characteristic of the phase transition at T=580 K. The dominant mechanisms of phonon heat transfer in the region of ferroelectric and antiferromagnetic phase transitions are considered. The temperature dependence of the average phonon mean free path is determined. Keywords: multiferroics, heat capacity, thermal diffusivity, thermal conductivity.

This paper aims to study of the variation of key thermal properties (thermal diffusivity, heat capacity, and derived values of thermal conductivity) of heavy oil saturated reservoir rock sample before and after high temperature treatment. A laser flash method (LFA 457) and differential scanning calorimeter (DSC 204 F1) were employed to study of the temperature effect on the thermal diffusivity ( ) and heat capacity ( ) of natural heavy oil reservoir rock sample. The measurements of the thermal – diffusivity have been made over the temperature range from (296 to 1023) K. The isobaric heat capacities of the same sample were measured in the temperature range from (299 to 768) K. Uncertainties of the measurements are 3 % and 1 % for and , respectively. The measurements were made in heating and cooling runs. Significant difference between the measured properties before and after thermal treatment was observed. Measured values of thermal diffusivity ( ) and heat capacity ( ) together with density data ( ) were used to calculate the derived very important properties of rock sample (thermal conductivities, ) using well-known thermodynamic relation, . A relationship between the temperature behavior of the thermophysical properties ( , , ) and the physical-chemical processes (thermal decomposition of pore heavy oil and volatilization of residual water absorbed in the pore walls) occurring in the rock pores during heating in distinct temperature ranges has been studied. The sig-nificant effect of thermal decomposition and dehydration processes on the temperature behavior of measured values of thermal -diffusivity and heat-capacity of oilbearing reservoir rock sample at high temperatures (above 680 K) was experimentally observed.

A laser flash method (micro-flash apparatus LFA 457) and differential scanning calorimeter (DSC 204 F1) were employed to study of the temperature effect on the thermophysical properties (thermal diffusivity $$a$$, heat capacity $$C_{\text{P}}$$ and thermal conductivity $$\lambda$$) of the natural reservoir rock sample. A relationship between the thermophysical properties behavior and the physical–chemical processes (thermal decomposition of pore heavy oil and volatilization of pore fluids) occurring in the rock’s pore fluids during heating in distinct temperature ranges was established. The measurements of the thermal-diffusivity have been made over the temperature range from 295 to 774 K. The isobaric heat capacities (CP) of the same sample were measured in the temperature range from 308 to 768 K. Uncertainties of the measurements are 3% and 1% for $$a$$ and $$C_{\text{P}}$$, respectively. The significant effect of thermal decomposition on the measured values of heat-capacity of reservoir rock sample at high temperatures (above 680 K) was experimentally found. We experimentally observed temperature anomaly of the heat capacity of rock sample in distinct temperature ranges, around 380 K (low-temperature range) and 680 K (high-temperature range).We attribute these anomalies to the dehydration (evolution of the volatile matter, VM, devolatilization) and aromatization of the carbon (thermal decomposition), which are known to occur under heat treatment. This leads to unusual increasing the heat capacity at high temperatures. Measured values of thermal diffusivity ($$a$$) and heat capacity ($$C_{\text{P}}$$) together with density data ($$\rho = { 2210}\;{\text{kg}}\;{\text{m}}^{ - 3}$$) were used to calculate the derived key properties, thermal conductivities ($$\lambda$$) of the rock sample, using very well-known relation, $$\lambda = a\rho C_{\text{P}}$$.

The thermal diffusivity and thermal conductivity of Bi1-xHoxFeO3 multiferroics (x = 0-0.20) were studied in the high-temperature range 300-1200K. It has been established that alloying with rare earth element with holmium leads to a noticeable increase in heat capacity in a wide temperature range T> 300 K and to a significant change in the temperature anomalies of thermal diffusion and thermal conductivity of the phase transition region. The dominant mechanisms of phonon heat transfer in the region of ferroelectric and antiferromagnetic phase transitions are considered. The dependence of the mean free path on temperature has been determined. Research results are discussed in conjunction with structural studies.

The thermal diffusivity and thermal conductivity of multiferroics Bi1 – xHoxFeO3 (x = 0–0.20) have been studied in the high-temperature region of 300–1200 K. It is established that alloying with the rare-earth element (holmium) strongly increases the specific heat in a wide temperature range T > 300 K and significantly changes temperature anomalies of the thermal diffusion and thermal conductivity near phase transitions. Dominant mechanisms of phonon heat transfer near the ferroelectric and antiferromagnetic phase transitions are considered. The temperature dependence of the mean free path is determined. The results obtained are discussed along with the structural investigation data.

As well-known the rate of heat extraction depends on the thermal conductivity, $$Q = - \, \lambda \left( T \right){\text{grad }}T$$, and the fluids flow characteristics, while amounts of heat recovery depends on heat capacity of reservoir rocks, $$Q = \left( {1 - \phi } \right)\rho C_{\text{P}} T$$, where $$\phi$$ is the porosity. In the present work the laser-flash (LFA 457) and differential scanning calorimeter (DSC 204 F1) techniques were employed on a heavy oil saturated natural rock sample for accurate measurements of the thermal diffusivity and heat capacity over a temperature range from (294 to 1024) K and from (306 to 771) K, respectively. The density of the sample at room temperature was 2300 kg m−3 and the porosity was 17.1%. The sample for the present study comes from Russian Oil Field (Eastern Siberia, Russia). The expanded uncertainty of the thermal diffusivity and heat capacity measurements at the 95% confidence level with a coverage factor of k = 2 is estimated to be 3% and 1%, respectively. At low temperatures (below approximately 373 K), the sharp increases (up to η = 2.3) of the thermal diffusivity anisotropy was observed. Based on the measured thermal diffusivity and heat-capacity data, thermal conductivity of the same oil saturated rock sample was calculated using the thermodynamic relation $$\lambda = a\rho C_{\text{P}}$$. The effect of temperature and various physical and chemical processes, such as thermal decomposition (chemical reactions) of pore heavy oil occurred in the sample during the heating in distinct temperature ranges were studied. The effect of pore heavy oil decomposition (under thermal stress) on the measured values of heat capacity and other thermophysical properties of rock sample at high temperatures (around 700 K) was experimentally observed. Also, we experimentally found weak temperature maximum of the heat-capacity of the sample under study in the low temperature range (around 380 K).

The paper presents the results of a comprehensive study of the thermophysical properties (thermal conductivity, thermal diffusivity, heat capacity) of high-temperature multiferroic BiFeO3 modified with rare-earth elements (REEs) (La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Lu). The regularities of the formation of the mentioned characteristics were established. The assumptions about the nature of the observed phenomena were suggested.

The effects of the modification of bismuth ferriteBismuth ferrite by various rare earth elementsRare Earth Elements (REE) (REE) are considered: the results of the investigation of the influence of crystal-physical parameters of stoichiometrically introduced dopants on the form of the phase diagrams of Bi1−xREExFeO3 systems, the grain structureGrain structure of ceramics, the dielectricDielectric spectra and thermal propertiesThermal properties of samples over a wide range of temperatures are presented.

3 Научно-исследовательский институт физики Южного федерального университета; Россия, Ростов-на-Дону, пр

The crystal structure and surface morphology of ceramics as well dielectric and thermal properties of Bi1−xErxFeO3 (where x = 0.05 − 0.20, Δх = 0.05) magnetoelectric solid solutions (SS) were investigated. The regularities of changes in phase composition, microstructure, electrical and dielectric properties of objects at room temperature are established.

We have studied the thermal diffusivity and thermal conductivity of Bi1 –xGdxFeO3 multiferroics within the high temperature range of 300–1200 K. We consider the dominant mechanisms of the heat transfer of phonons within the domain of ferroelectric and antiferromagnetic phase transitions and determine the temperature dependence of the mean free path of the phonons.

The paper presents the results of a comprehensive study of the crystal structure, grain structure, dielectric and thermal properties of high-temperature multiferroics Bi1-x(Nd, Pr)(x)FeO3 (concentration interval x = 0.00-0.50). The regularities of the formation of the phase and grain structure, electrical and dielectric properties of objects at room temperature were established. The assumptions about the nature of the observed phenomena were suggested.

A study of thermal diffusion, heat capacity and thermal conductivity of multiferroic Bi1-xEuxFeO3 (x = 0-0.4) within the range of 130-1200 K is reported. Modifying by admixture of Eu is found to change substantially the thermal anomalies of diffusion and thermal conductivity of the antiferromagnetic phase transition, to increase heat capacity over a wide range of temperatures and to shift the antiferromagnetic transition temperature. The excess heat capacity is shown being related to Schottky effect of three-level states. The mechanisms dominating thermal transfer of phonons at the phase transition and dependence of the mean free path of phonons on the temperature are determined. The results are discussed with account of structural data. (C) 2016 Elsevier B.V. All rights reserved.