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Local octahedral tilts in La 2 − x Ba <mml…

1994; American Physical Society; Volume: 72; Issue: 14 Linguagem: Inglês

10.1103/physrevlett.72.2282

1092-0145

Simon J. L. Billinge, G. H. Kwei, H. Takagi,

Theoretical and Computational Physics

The short-range structure in ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ba}}_{\mathit{x}}$${\mathrm{CuO}}_{4}$ is examined by obtaining the pair distribution function from neutron powder diffraction data. In contrast to the predictions of the crystal structure models, locally, the ${\mathrm{CuO}}_{6}$ octahedra do not change their tilt direction at the low-temperature tetragonal (LTT) to low-temperature orthorhombic (LTO) phase transition: they always tilt in the [110] (LTT) directions. The long-range structures of the high-temperature phases result from coherent superpositions of the local LTT variants. The local tilt order extends over \ensuremath{\sim}1 nm. We discuss the implications of this local structure for the properties.