Simultaneous measurement of the influence of the electric field on specific heat, thermal conductivity and pyroelectric coefficient is described as a summary of previous papers. From these coefficients, which are determined by means of a flux calorimeter, the behaviour of other properties, such as thermal diffusivity and electrocaloric coefficient, is deduced.
Authors:J. Igartua, G. Aguirre-Zamalloa, I. Ruiz-Larrea, M. Couzi, A. López-Echarri, and T. Breczewski
The specific heat of N(CH3)4CdBr3 from 50 to 300 K has been measured by adiabatic calorimetry, using both static and dynamic methods. The obtained results
have permitted a careful study of the ferro-paraelectric phase transition the crystal shows at 160 K. The available spectroscopic
data have been used to generate a reliable baseline which accounts for the normal lattice contribution to the specific heat.
These results allow for an accurate estimation of the phase transition thermodynamic functions: ΔH=2620 J·mol−1 and ΔS=18.04 J·(mol°C)−1. These high values are in agreement with the predictions of the 6 well potential Frenkel model.
Authors:K. Süvegh, A. Domj'an, R. Tarsoly, and A. Vértes
BaTiO3, was studied by positron lifetime spectroscopy in static electric fioeld. The strength of the field was varied from 0 up to 104 V/cm. Two characteristic points were found at 4500 V/cm and at 8500 V/cm. These field strengths were related to subsequent ordering processes of the crystal. Additional temperaturee dependent measurements were perforrmed in the 70–310 range to confirn the interopretaion of the two positron lifetimes. The two expected phase transitions were observed and these measurements showd that positron are trapped by Ba vacancies.
Raw chemicals such as metal nitrates and chlorides were found to affect the thermal decomposition behaviour of EDTA-gel precursors
used for the production of ceramic powders. Fine, homogeneous ceramic powders were produced from nitrate solutions while chlorides
gave segregated phases. In studies on the production of lead zirconate titanate (PZT) using chlorides, the segregation and
loss of lead was observed and shown to be caused by the formation and evaporation of PbCl2. Thermal analysis (DTA/TG) quantitatively proved the suggested reaction mechanism for this phase segregation. Crystallization
of the desired perovskite phase of lead zirconate titanate (PZT) and barium titanate (BT) initiated at temperatures as low
as 250°C in the nitrate-EDTA precursors. Water of crystallization and formation of BaCO3 in the barium titanate precursor were suggested to account for differences in the observed decompositional behaviours of
the BT and PZT precursors.
Authors:M. E. Kassem, A. M. El-Khatib, E. A. Ammar, and M. M. Denton
Thermodynamic studies of (LixK1−x)2SO4, LKS, mixed crystals have been made in the concentration range (x=0.1, 0.2, ...,x=0.5). The thermal behaviour has been investigated by differential thermal analysis, DTA, and differential scanning calorimeter, DSC, in the vicinity of high temperature phases. Also, the effect of the thermal neutron irradiations on the thermal properties of mixed crystals was studied. The results showed a change in the transition temperatureTc, as well as the value of specific heatCp at transition temperature, due to the change of stoichiometric ratio and radiation doses. The change of enthalpy and entropy of mixed crystals have been estimated numerically.
Authors:Hengfeng Li, Kaiyuan Tan, Zeming Hao, and Guowen He
Poly(vinylidene fluoride) (PVDF) based ferroelectric polymers are technologically important thermoplastics, which find a variety of applications in advanced electromechanical devices such as capacitors, transducers
Both temperatures, TC, (TC —Curie temperature) and heat of the phase transition: ferroelectric-paraelectric, ΔH, in the BaxSr1−xTiO3 materials have been studied by means of the microcalorimetric method. The determined parameters were verified by either temperature
dependence of the dielectric permittivity (Curie-Weiss law) or thermodynamic method. The effect of strontium content on TC has been discussed. It was found that microcalorimetry is useful tool studying phase transition phenomena in ferroelectric
Authors:K. Katok, V. Tertykh, V. Yanishpolskii, A. Ragulya, V. Klimenko, and D. Klymchuk
Matrix isolation of ferroelectric BaTiO3 nanoparticles was executed by formation of protective silica shell (via hydrolysis and polycondensation of tetraethyl orthosilicate)
on particles of precursor—barium titanyl oxalate. Synthesized BaTiO3–SiO2 composites have been characterized by IR spectroscopy, XRD, TEM, DTA/DTG methods.