KYHP3O10: Rietveld refinement using X-ray powder diffraction data and Raman study of the conductivity phase transition

摘要

Potassium yttrium hydrogen triphosphate (KYHP3O10) crystallises in the triclinic system P1 at room temperature with the following parameters: a = 6.8522(2), b = 7.6254(2), c = 8.5351(2) Angstrom, alpha = 106.658(1), beta = 106.435(2) and gamma = 82.344(2)degrees; Z = 2. This structure has been refined from X-ray powder diffraction data using the Rietveld method, with the isostructural compounds KSmHP3O10 and NH4Bi3O10 as the starting model. Refinement of 70 parameters by the Rietveld method, using 2447 reflections, led to cR(wp) = 0.138, cR(p) = 0.104 and R-B = 0.041. This compound is a chain-based structure. The K+ and Y3+ cations are intercalated between chains, formed of (HP3O104-) groups linked by (OHO)-O-... hydrogen bonding along the c-axis. The yttrium atoms are in an eight-fold coordination and also build infinite chains of edge-sharing YO8 polyhedra running parallel to the a-axis. The potassium cations are coordinated by 10 oxygen atoms and build chains of KO10 polyhedra running parallel to the b-axis. A calorimetric study of the title compound shows one endothermal peak, which is detected at 519 K. Samples were examined by impedance and Raman spectroscopy techniques. The Raman spectra of KYHP3O10, recorded at different temperatures in the frequency range 50-1250 cm(-1) show the presence of a transition, which is characterised by an unusual high conductivity caused by breaking of the hydrogen bridges and suggests a great dynamic disorder of protons. This permits H+ ions at high temperature to contribute with the potassium cations to the ionic conductivity of the product. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 18]