Order-disorder and mobility of Li+ in the β′ and β-LiZr2(PO4)3 ionic conductors:: A neutron diffraction study

被引:50
作者
Catti, M
Morgante, N
Ibberson, RM
机构
[1] Univ Milan Biocca, Dipartimento Sci Mat, I-20125 Milan, Italy
[2] Rutherford Appleton Lab, ISIS Facil, CLRC, Didcot OX11 0QX, Oxon, England
关键词
neutron diffraction; Rietveld refinement; ionic conductivity; LiZr2(PO4)(3);
D O I
10.1006/jssc.2000.8658
中图分类号
O61 [无机化学];
学科分类号
070301 ; 081704 ;
摘要
Neutron diffraction profiles at high resolution (HRPD, ISIS Facility, U.K.) were collected on powder samples of LiZr2(PO4)(3) at 20 degrees C (beta' phase, monoclinic P2(l)/n, Z = 4; a = 8.81277 (4), b = 8.94520 (5), 12.37540 (6) Angstrom, beta = 90.801 (1)degrees) and at 350 degrees C (beta phase, orthorhombic Pbna, Z = 4; a = 8.84303 (5), b = 8.94120 (6), c = 12.41301 (8) Angstrom). All Li sites were located by difference Fourier maps in tetrahedral coordination, and both structures were Rietveld-refined to wR(p) = 0.0353 (beta') and 0.0429 (beta), The beta' structure is a distortion of beta, with a [100] pseudo-twofold axis x, 1/2 - y, - z relating all atoms but lithium, which is fully ordered (< Li-O > = 2.02 Angstrom). In the beta phase, Li is disordered over four sites, of which two (Li1 and Li2) are symmetry-independent with occupancies 0.34 (1) and 0.16 (1), respectively, and < Li-O > = 2.17 and 2,16 Angstrom, The disorder fully explains the higher Li+ mobility in the beta with respect to the beta' phase observed from ionic conductivity data. Mechanisms of ion transport are proposed, and the relationship to the NASICON-type alpha'/alpha phase of LiZr2(PO4)(3) is analyzed in detail. (C) 2000 Academic Press.
引用
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页码:340 / 347
页数:8
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