Mossbauer effect in ferroelectric BaTiO₃

Abstract

The mossbauer effect for Fe^57m in the BaTiO₃ lattice has been studied from 300 to 1200°K with particular emphasis on the region near the Curie temperature. The mossbauer probe seems to serve as a useful tool for the study of ferroelectrics. The electric-field gradient as seen by the probe at room temperature is -0.52×10¹⁴ esu cm^-3 and is closely proportional to P_s² as the spontaneous polarization P_s varies with temperature. The strength of the resonant absorption was also determined as a function of temperature in the region above T_c. Much above T_c these measurements are compatible with a Debye temperature of 450°K. However, as the Curie temperature is approached, the lamb-mossbauer factor decreases appreciably. These results are discussed in the light of Cochran's theory of ferroelectricity. From the isomer shift at room temperature (0.50±0.02 mm/sec with respect to 310 stainless steel) the over-all degree of ionicity is estimated to be 60±20%. The temperature shift shows a discontinuity at T_c and is attributed to the change in covalent binding.