Sr 2 SbMnO 6 : A new semiconductor ferroelectric

Sr 2 SbMnO 6 is predicted to be ferroelectric with Curie temperature Tc=450(175) K on the basis of a 1990 structure determination. Calorimetry reveals a stepwise heat capacity change at Tc=431(5) K, indicative of a phase transition close to first order. A further small calorimetric anomaly occurs reproducibly at 743(10) K, consistent with an earlier report of a higher-temperature phase transition to cubic symmetry. The dielectric permittivity ε′ increases sharply at Tc=466(10)K in the range 0.1–100 kHz; ε′ rises ∼3 orders of magnitude at 0.1 kHz, ∼1.0 order at 100 kHz, before a stable maximum is reached at T>Tc. The conductivity σ of Sr2SbMnO6 at 295 K is 0.23(5) S m−1, too high for dielectric hysteresis measurement. The linear dependence of ln σ on 1/T between 295 K and Tc in this semiconductor ferroelectric corresponds to a band-gap EG=0.50(2) eV; above Tc, EG increases abruptly to 0.70(2) eV.