A Mixed {alpha}/{beta} Superstructure in NASICON Ionic Conductors: Neutron Diffraction Study of Li

Journal Article · Thu Feb 01 04:00:00 EST 2001 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1006/jssc.2000.8999· OSTI ID:784083

Catti, Michele

The lithium conductors Li{sub 2}FeTi(PO{sub 4}){sub 3} and Li{sub 2}FeZr(PO{sub 4}){sub 3}, synthesized by solid-state reaction and characterized by X-ray powder diffractometry, were studied structurally at room temperature by neutron powder diffraction at high resolution (HRPD, ISIS Facility, U.K.). By trial-and-error and Rietveld refinements (R{sub p}=0.111, R(F{sup 2})=0.112), the first compound (orthorhombic Pbca, Z=8; a=8.5515(1), b=8.6229(1), c=23.9116(3) {angstrom}) was shown to have a complex superstructure sharing features of both the {alpha} and {beta} NASICON-type phases of LiZr{sub 2}(PO{sub 4}){sub 3}. Four (001) layers of PO{sub 4} and (Fe, Ti)O{sub 6} polyhedra are present per unit-cell, and they are related both by -1 inversion centers ({alpha} structure) and by a glide planes ({beta} structure). Ti{sup 4+} and Fe{sup 3+} order in the two interlayer regions, respectively. Owing to the structure complexity, only half of the lithium atoms could be refined in tetrahedral coordination with < Li-O > =1.99 {angstrom}. Li{sub 2}FeZr(PO{sub 4}){sub 3} (orthorhombic Pbna, Z=4; a=8.70559(8), b=8.78572(9), c=12.2202(1) {angstrom}) proved to be similar to {beta}-LiZr2(PO4)3; however, by Fourier synthesis and Rietveld refinement (R{sub p}=0.0618, R(F{sup 2})=0.0574) Li was located in a fully ordered tetrahedral configuration with < Li-O >=2.01 {angstrom}, instead of being disordered as in the phase of LiZr{sub 2}(PO{sub 4}){sub 3}.

• Research Organization: Dipartimento di Scienza dei Materiali, Universita di Milano Bicocca, Milano (IT)
• Sponsoring Organization: Ministero per l'Universita e per la Ricerca Scientifica e Tecnologica (Italy); Consiglio Nazionale delle Ricerche (Italy) (US)
• OSTI ID: 784083
• Journal Information: Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: 2 Vol. 156; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ATOMS
CHEMICAL PREPARATION
CONFIGURATION
DIFFRACTION
EXPERIMENTAL DATA
IONIC CONDUCTIVITY
IRON PHOSPHATES
LATTICE PARAMETERS
LITHIUM
LITHIUM IONS
LITHIUM PHOSPHATES
NEUTRON DIFFRACTION
NEUTRONS
ORTHORHOMBIC LATTICES
PHOSPHATES
RESOLUTION
SPACE GROUPS
SYNTHESIS
TITANIUM PHOSPHATES
X-RAY DIFFRACTION
ZIRCONIUM PHOSPHATES