On the crystal structures of SrTeO3

SrTeO3 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 degrees C. The SrTeO3 low temperature (22 degrees C) form was found (R-wp = 1.49%, chi(2) = 1.06) to crystallize in space group C2/c with the unit cell parameters a = 28.133(9) angstrom, b = 5.9044(15) angstrom, c = 28.418(6) angstrom, beta = 114.303(17)degrees. 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 Te4+ 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 TeO3E pyramids do not connect to each other; instead they share their oxygen atoms with Sr polyhedra. The discontinuous change of the SrTeO3 lattice parameters in the region 260-310 degrees 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 degrees C no evidence of lowering of the symmetry was found. The structure model of the SrTeO3 high temperature (410 degrees 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. (c) 2006 Elsevier SAS. All rights reserved.