Intrinsic inhomogeneity as origin of incomplete ferroelectricityA. Bussmann-Holder1 and A. R. Bishop2
1 Max-Planck-Institute for Solid State Research - Heisenbergstr. 1 D-70569 Stuttgart, Germany
2 Los Alamos National Laboratory, Theoretical Division Los Alamos, NM 87545, USA
received 10 July 2006; accepted in final form 16 October 2006
published online 10 November 2006
Strontium titanate is an incipient ferroelectric where the freezing of the soft polar mode is inhibited by quantum fluctuations (MÜLLER K. A. and BURHARD H., Phys. Rev. B, 19 (1979) 3593). Exchanging 16O by its isotope 18O induces ferroelectricity at (ITOH M., WANG R., INAGUMA Y., YAMAGUCHI T., SHAN Y. J. and NAKAMURA T., Phys. Rev. Lett., 82 (1999) 3540). This finding is unexpected and its origin remains unclear since seemingly contradictory data have been obtained. Here we suggest that SrTi18O3 (STO18) exhibits self-induced intrinsic inhomogeneity due to optic - acoustic mode coupling, whereby dynamical clusters are formed with a lower symmetry than the embedding matrix. With decreasing temperature these clusters grow in size and volume fraction and remain present in the ferroelectric state leading to an incomplete ferroelectric ground state. The remaining lattice shows soft-mode behaviour. Since the length and time scales of the coexisting components differ considerably, experiments which test these scales can reach contradictory conclusions concerning the phase transition mechanism.
77.80.Bh - Phase transitions and Curie point.
77.80.-e - Ferroelectricity and antiferroelectricity.
77.84.-s - Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials.
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