Berlin 2012 – scientific programme

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DF: Fachverband Dielektrische Festkörper

DF 7: 100 years since the Laue experiment: Topical aspects of diffraction and scattering (Joint Session KR, BP, CPP, DF, GP, MA, MI, MM; related to SYXD)

DF 7.9: Talk

Tuesday, March 27, 2012, 12:00–12:15, EMH 225

Monoclinic Symmetry in Barium Titanate — Christian Eisenschmidt, •Hans Theo Langhammer, and Günther Schmidt — Martin-Luther-Universität Halle-Wittenberg, Institut für Physik

The tetragonal-orthorhombic phase transition of barium titanate crystals has been investigated by XRD measurements during slow cooling. Additional diffuse scattering intensity between the (002) and (200) reflexes as well as a shift of the (200) reflex towards higher 2Θ values develop with decreasing temperature and time. The tetragonal-orthorhombic phase transition takes place obviously via a monoclinic intermediate stage. This can be understood by assuming this order-disorder phase transition is initiated by increasing short-range order (SRO) of Ti ions followed by rearranging of Ba ions similar to the 'tetragonal' SRO below the Burns temperature above the transition cubic-tetragonal. This results, finally, in nucleation and transition to the long-range ordered orthorhombic phase. Conclusions of the proposed mechanism in compositionally disordered systems like Ba(Ti,Sn)O3, PMN-PT et al. are discussed.