Mossbauer effect in ferroelectric BaTiO<SUB>3</SUB>

The mossbauer effect for Fe<SUP>57m</SUP> in the BaTiO<SUB>3</SUB> lattice has been studied from 300 to 1200&#176;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&#215;10<SUP>14</SUP> esu cm<SUP>-3</SUP> and is closely proportional to P<SUB>s</SUB><SUP>2</SUP> as the spontaneous polarization P<SUB>s</SUB> varies with temperature. The strength of the resonant absorption was also determined as a function of temperature in the region above T<SUB>c</SUB>. Much above T<SUB>c</SUB> these measurements are compatible with a Debye temperature of 450&#176;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&#177;0.02 mm/sec with respect to 310 stainless steel) the over-all degree of ionicity is estimated to be 60&#177;20%. The temperature shift shows a discontinuity at T<SUB>c</SUB> and is attributed to the change in covalent binding