Simultaneous measurements of specific heat capacity and dielectric constant of ferroelectric SrBi₂(Nb_x Ta_1-x)₂O₉ ceramics

Abstract

Simultaneous measurements of specific heat capacity and dielectric constant have been performed for ferroelectric SrBi₂ (Nb_x, Ta_1—x)₂O₉ ceramics with bismuth layer-structure. An apparatus based on thermal radiation calorimetry was used in the present measurement. Following the Stefan-Boltzmann law, a disk-shaped sample with blackened surfaces was taken through heating and cooling modes in a vacuum chamber. Heating was performed using double flat heaters. The specific heat capacity is obtained only from the sample temperature, the heater radiative power, and the time rate of the sample temperature change on both modes, while the dielectric constant was measured using an inductance-capacitance-impedance meter at 1 MHz. Anomalies in the specific heat capacity were observed near the transition temperature expected from the simultaneous dielectric measurement. The Curie temperatures of SrBi₂(Nb, Ta)₂O₉ ceramics determined from the experimental results are 10 ∼ 20° C lower than those obtained by previous authors.

Keywords:

• Specific heat capacity
• dielectric constant
• calorimetry
• ferroelectric phase transition
• bismuth layer-structured ferroelectricity (BLSF)