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 °C. The SrTeO3 low temperature (22 °C) form was found (Rwp=1.49%Rwp=1.49%, χ2=1.06χ2=1.06) to crystallize in space group C2/c with the unit cell parameters a=28.133(9) Åa=28.133(9) Å, b=5.9044(15) Åb=5.9044(15) Å, c=28.418(6) Åc=28.418(6) Å, β=114.303(17)°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 TeO bond lengths. The Te4+ lone-pair (E) plays an active stereochemical role. The SrO 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 °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 SrTeO3 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.

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