Morphotropic transitions in the rare-earth trifluoride series

Journal Article · Wed Mar 01 04:00:00 EST 1995 · Crystallography Reports

OSTI ID:255069

Fedorov, P P; Sobolev, B P ^[1]

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1. Shubnikov Institute of Crystallography, Moscow (Russian Federation)

Phase transformations in the rare-earth trifluorides (RF{sub 3}) series were analyzed. Taking into account the thermochemical and experimental data on the phase diagrams of the MF{sub n}-RF{sub 3} binary systems, the metastable-melting temperatures for the competing structural types in this series were calculated. In the row of rare-earth compounds the melting points of the phases with the LaF{sub 3} and {beta}-YF{sub 3} structures show a jump between gadoliniurn and terbium, resulting in an inversion of the relative stabilities of these structure types. For the RF{sub 3} compounds of the cerium (R is La to Gd) and yttrium (R is Th to Lu) groups, the model of an ideal morphotropic series may be applied, i.e., the Gibbs free energies are smooth functions of the ionic radii. For R from Sm to Gd, the temperatures of the {beta}-YF{sub 3} {r_reversible} tysonite polymorphic transformation is described by the equation T[K] = 3160(1.226 - r){sup 0.284}, where r (A) is the Shannon ionic radius. Neither NdF{sub 3} nor PmF{sub 3} has low-temperature polymorphs of the {beta}-YF{sub 3} structure type. 46 refs., 4 figs., 5 tabs.

• OSTI ID: 255069
• Journal Information: Crystallography Reports, Journal Name: Crystallography Reports Journal Issue: 2 Vol. 40; ISSN CYSTE3
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CRYSTAL STRUCTURE
FLUORIDES
FREE ENERGY
MORPHOLOGICAL CHANGES
PHASE DIAGRAMS
PHASE TRANSFORMATIONS
RARE EARTH COMPOUNDS