On the crystal structures of SrTeO 3

Abstract

SrTeO 3 has been studied by powder neutron diffraction (PND) experiments and by second harmonic generation (SHG) method at a series of temperatures between 20 and 560 °C. The SrTeO 3 low temperature (22 °C) form was found ( R wp = 1.49 % , χ 2 = 1.06 ) to crystallize in space group C2/c with the unit cell parameters a = 28.133 ( 9 ) Å , b = 5.9044 ( 15 ) Å , c = 28.418 ( 6 ) Å , β = 114.303 ( 17 ) ° . The Sr atoms are coordinated by six, seven or eight oxygen atoms. Each Te atom has a similar ‘pyramidal’ geometry, coordinated by three oxygen atoms having similar Te O bond lengths. The Te 4+ lone-pair (E) plays an active stereochemical role. The Sr O polyhedra form an openwork framework with 2 types of channels. Inside the channels the tellurium atoms are located. The TeO 3E pyramids do not connect to each other; instead they share their oxygen atoms with Sr polyhedra. The discontinuous change of the SrTeO 3 lattice parameters in the region 260–310 °C and abrupt growth of SHG signal in this temperature region correspond to the onset of the ferroelectric phase in a first-order phase transition. However from the diffraction data acquired at 410 °C no evidence of lowering of the symmetry was found. The structure model of the SrTeO 3 high temperature (410 °C) modification is proposed in the same space group C2/c. The plausible reasons of the discrepancy between the PND and SHG results are discussed.