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.

The temperature dependence of the heat capacity of the CoFe2O4 ferromagnet and the 0.3CoFe2O4-0.7PbTiO3 multiferroic composite in the temperature range 150-820 K has been studied. heat capacity over a wide temperature range. It is noted that the additional component of the heat capacity is due to the transition of cobalt or iron ions to higher energy levels, as well as due to the distortion of the lattice parameters due to the appearance of three coexisting phases. Keywords: heat capacity, multiferroic composite, Schottky effect.

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.

The temperature dependence of the heat capacity of the CoFe2O4 ferromagnet and the 0.3CoFe2O4–0.7PbTiO3 multiferroic composite in the temperature range 150–820 K has been studied. heat capacity over a wide temperature range. It is noted that the additional component of the heat capacity is due to the transition of cobalt or iron ions to higher energy levels, as well as due to the distortion of the lattice parameters due to the appearance of three coexisting phases.

The temperature dependence of the specific heat of the CoFe2O4 ferromagnet and the 0.3CoFe2O4–0.7PbTiO3 muliferroic composite is studied in the temperature range 150–820 K. An addition of lead titanate ferroelectric to cobalt ferrite ferromagnet is found to lead to a shift of the magnetic phase transition temperature to lower temperatures by 49 K and to a decrease in the specific heat in a wide temperature range. It is noted that the additional component of the specific heat is due to transitions of cobalt or iron ions to higher energy levels and also due to a distortion of the lattice parameters as a result of formation of three coexisting phases.

The temperature dependence of the heat capacity of nanostructured SmFeO3 ceramics obtained by mechanical activation in the temperature range of 120-800 K has been studied. It has been shown that the excess heat capacity of mechanically activated ceramics is due to: displacements of iron and samarium ions and with a change in the angle between FeO6 oxygen octahedra. Keywords: multiferroics, heat capacity, samarium ferrite, Schottky heat capacity, nanostructured ceramics, mechanical activation.

The temperature dependence of the heat capacity of nanostructured SmFeO3 ceramics obtained by mechanical activation in the temperature range of 120–800 K has been studied. It has been shown that the excess heat capacity of mechanically activated ceramics is due to: displacements of iron and samarium ions and with a change in the angle between FeO6 oxygen octahedra.

Studies of the heat capacity and dielectric properties of (1-x)BiFeO 3-x PbFe 0.5 Nb 0.5 O 3 ceramic multiferroics in the temperature range of 300-800 K were carried out. Based on studies of the temperature and concentration dependences of the heat capacity and dielectric constant, the phase transition temperatures of the (1-x)BiFeO 3 system were determined. (1-x)PbFe 0.5 Nb 0.5 O 3 with various x concentrations. It is shown that with an increase in the PbFe 0.5 Nb 0.5 O 3 component, the temperatures of the ferroelectric and antiferromagnetic transitions in BiFeO 3 shift to low temperatures. Taking into account structural studies, a "temperature-concentration" phase diagram has been constructed. Keywords: heat capacity, dielectric properties, ferromagnet, antiferromagnet, multiferroics.

Studies of the heat capacity and dielectric properties of (1-x)BiFeO3-xPbFe0.5Nb0.5O3 ceramic multiferroics in the temperature range of 300-800 K were carried out. Based on studies of the temperature and concentration dependences of the heat capacity and dielectric constant, the phase transition temperatures of the (1-x)BiFeO3 system were determined. -xPbFe0.5Nb0.5O3 with various x concentrations. It is shown that with an increase in the PbFe0.5Nb0.5O3 component, the temperatures of the ferroelectric and antiferromagnetic transitions in BiFeO3 shift to low temperatures. Taking into account structural studies, a "temperature-concentration" phase diagram has been constructed.

In this work, the influence of simultaneous action of high pressure and shear deformation (mechanical activation) on the physical properties of synthesized YbFeO3 was studied using complex methods. The formation of crystalline structures of YbFeO3 powders with different concentrations of structural defects was carried out using Bridgman anvils. It was found that during mechanical activation, the tilting angles of FeO6 oxygen octahedra change within the range θ = 12.69–28.45°. Using X-ray diffraction, it was established that the linear unit cell parameters a, b and c change in a consistent manner with changing mechanical activation pressure, while the space-group symmetry $${D}_{2h}^{16}$$ –Pbnm is preserved. The sizes of the coherent scattering regions (D) decrease by more than 90% at the maximum mechanical activation pressure (1200 MPa). It was found that the mechanical activation pressures of YbFeO3 have a threshold value (800 MPa), above which the dislocation density decreases. According to the results of impedance spectroscopy, the nature of relaxation was found to be non-Debye and the activation energy increased from 0.649 eV for the starting sample to 1.395 eV for the sample mechanically activated sample at 1 GPa. The magnetization curves M(H) were described using the law of approach to magnetic saturation (LAS), and the critical crystallite size (Dcr) was determined to be 50 nm, at which the maximum Hc is observed. The behaviors of the spectroscopic splitting factor (g) and half-width (ΔH) of the electron paramagnetic resonance (EPR) spectrum are analogous to Hc and Mr, however, the maximum ΔH is observed in the range of 50–105 nm, and the g-factor reaches its maximum at particle sizes of 105 nm.

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.

The temperature dependence of the heat capacity of the multiferroics BiFeO3, Bi0.90Sm0.10FeO3, and Bi0.90Eu0.10FeO3 has been studied. It was found that the substitution of europium and samarium ions for bismuth ions in bismuth ferrite leads to the appearance of an additional heat capacity component due to transitions of 4f - electrons of rare earth ions to higher levels of the multiplet. A connection is established between the decrease in phonon thermal conductivity and the Schottky effect for the specific heat.

The temperature dependence of the heat capacity of multiferroics BiFeO3, Bi0.90Sm0.10FeO3, and Bi0.90Eu0.10FeO3 has been investigated. It is found that the substitution of bismuth ions with europium and samarium ions in bismuth ferrite leads to the appearance of an additional heat capacity component due to the transitions of 4f electrons of rare earth ions to higher multiplet levels. A relationship is established between the decrease in phonon thermal conductivity and the Schottky effect for the specific heat.

It has been shown that structural defects can play a dominant role in the formation of the physical properties of ceramics. This paper presents the results of studying the physical properties of Er3Fe5O12 (ErIG) powders and ceramics, containing the structural defects of various types. The formation of the structural defects in ErIG was achieved by the mechanical activation of pre-synthesized powders using Bridgman anvils, to which fixed shear strain and uniaxial pressures of various magnitudes were applied in the range of 40–320 MPa. The lower anvil rotated at the speed of 3 revolutions per hour (rph). The structural parameters of the mechanically activated powders and ceramics sintered from them were studied at room temperature by the X-ray method. The band gap was determined by the optical spectroscopy, the magnetic properties were estimated from the hysteresis loops and the dielectric properties and heat capacity were studied in the high-temperature range. It has been established that mechanical activation leads to a significant smearing of antiferrimagnetic transition and to a shift in the phase transition temperature to the low-temperature region.

On the basis of experimental studies (in situ) of the electrical resistance and thermal expansion of the Ti67 Al33 intermetallic compound in a metastable and stabilized state, the relationship between the temperature coefficients of athermal electrical resistance (TCAR) and thermal expansion (TCE) is shown. This relationship is universal because it is preserved under transitions from one state to another. The anomalies associated with the competition between the metallic and semiconducting types of conductivity observed in the TCAR, TEC and heat capacity curves coincide in temperature.

The article discusses the effects of modifying bismuth ferrite BiFeO3 with rare-earth elements, REE, (large-sized, group 1, with 0.94 ≤ ≤ 1.04 Å – La, Pr, Nd, Sm, Eu, Gd, medium-sized, small-sized Group 2, with <0.94 Å – Tb, Dy, Ho, Er, Tu, Yb, Lu). The authors describe the study results of the influence of the crystallophysical parameters of stoichiometrically introduced dopants on the type of phase diagrams of Bi1-xREExFeO3 systems, the grain structure of ceramics, the dielectric spectra of samples, and the behaviour of their thermophysical characteristics over a wide temperature range. They show the possibility of using new multiferroic materials in artificial intelligence systems.

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, $$\lambda = a\rho C_{\text{P}}$$.