SR2SBMNO6 - A NEW SEMICONDUCTOR FERROELECTRIC

Sr2SbMnO6 is predicted to be ferroelectric with Curie temperature T-c = 450(175) K on the basis of a 1990 structure determination. Calorimet ry reveals a stepwise heat capacity change at T-c = 431(5) K, indicati ve of a phase transition close to first order. A further small calorim etric anomaly occurs reproducibly at 743(10) K, consistent with an ear lier report of a higher-temperature phase transition to cubic symmetry . The dielectric permittivity epsilon' increases sharply at T-c = 466( 10)K in the range 0.1-100 kHz; epsilon' rises similar to 3 orders of m agnitude at 0.1 kHz, similar to 1.0 order at 100 kHz, before a stable maximum is reached at T> T-c. The conductivity sigma of Sr2SbMnO6 at 2 95 K is 0.23(5) S m(-1), too high for dielectric hysteresis measuremen t. The linear dependence of ln sigma on 1/T between 295 K and T-c in t his semiconductor ferroelectric corresponds to a band-gap E-G = 0.50(2 ) eV; above T-c, E-G increases abruptly to 0.70(2) eV. (C) 1997 Americ an Institute of Physics.