Successive Jahn-Teller Phase Transitions in K_2PbCu (NO_2)_6

概要

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The successive phase transitions in K.PbCu(NO.), have been studied byprecise X-ray and neutron measurements. In phase II, we have observed thesatellite reflections at (7#.50.4l6, Al'f0.430,0) around each fundamental Braggreflection. In phase III, we have observed the superlattice reflections, instead ofthe satellite reflections of phase II, at (w.+8, A.l.J, L44-). This fact indicatesthat the crystal undergoes the successive phase transitions as normal->incommensurate->commensurate phase. The mode analysis of the Jahn-Telleractive phonon mode was carried out and the experimental intensity distributionof satellite and super lattice reflections were analysed from the standpoint of thecondensation of the phonon mode. The displacements in phase II is explained asthe condensation of the transverse acoustic mode as well as the optical modecompatible with local Jahn-Teller active mode with the wave vector k.=(0.42,0.43, 0), while these in phase III is explained as the condensation of the samemodes with k.=(1/2, 1/2, 1/'2.).
社団法人日本物理学会の論文
1978-09-15