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Structural Phase-Transitions of Rubidiumpolyphosphate, Rb2(X)(1)[P2o6]

Zeitschrift Fur Kristallographie 209(4): 322-327

Autoren/Herausgeber: Holst C
Schmahl WW
Fueß H
Erschienen: 1994

High temperature X-ray powder diffraction measurements of rubidiumpolyphosphate, Rb2{infinity/1}[P2O6] were carried out with a position sensitive detector (PSD) and analysed by the Rietveld method. Three new high temperature phases were identified. The monoclinic (P 2(1)/n, a = 12.1249(3) angstrom, b = 4.2279(1) angstrom, c = 6.4761(2) angstrom, beta = 96.006(2)-degrees room-temperature modification RbPO3-T, transforms at T(c) = 661 K to orthorhombic RbPO3-H (Pbnm) with the lattice constants a = 13.1674(4) angstrom, b = 4.5657(1) angstrom and c = 6.1183(2) angstrom (750 K). A continuous transition at T(c) = 914 K leads to RbPO3-HT (Bbmm, 940 K) with a = 13.3517(4) angstrom, b = 4.5917(1) angstrom and c = 6.1665(2) angstrom, for which the empirical power law behaviour of the order parameter Q is Q approximately (T - T(c))beta with beta near 0.2 for T(c) > T > 0.8 T(c). There are saturation effects below 0.8T(c).|The T --> H transition shows a hysteresis of ca. 110 K and on cooling an intermediate phase, RbPO3-Z, occurs at 591 K, with space group P 2(1)/n, a = 14.3476(5) angstrom, b = 4.5730(1) angstrom, c = 12.0839(4) angstrom and beta = 65.604(2)-degrees, which transforms back to the RbPO3-T state at.550 K.