POLYMORPHISM OF ABO$sub 3$ TYPE RARE EARTH BORATES

Journal Article · Fri Sep 01 00:00:00 EDT 1961 · Am. Mineralogist

OSTI ID:4837074

Levin, E M; Roth, R S; Martin, J B

Polymorphic relations were investigated as functions of temperature and ionic radius for 13 ABO/sub 3/ type borates, including all of the normally trivalent rare earth ions as well as La/sup 3+/, Y/sup 3+/, In/sup 3+/, and Mn/ sup 3+/. The melting points of the compounds varied irregularly from 1660 deg C for LaBO/sub 3/ to 1540 deg C for EuBO/sub 3/. In general, the borate compounds exhibited the same structure types as the three forms of CaCO/sub 3/, aragonite, vaterite, and calcite. Compounds of the larger ions, LaBO/sub 3/ and NdBO/sub 3/ , showed the aragonite-type structure at low temperature. These compounds were found to have a reversible transformation at 1488 and 1090 deg C, respectively. The high temperature forms were different, and both exhibited low symmetry. The following bora/sub 3/wed a stable vaterite-type phase: SmBO/sub 3/, EuBC3, GdBO/ sub 3/, DyBO/sub 3/, YBO/sub 3/, HoBO/sub 3/, ErBO/sub 3/, TmBO/sub YbBO/sub 3/, and LuBO/sub 3/. Above 1285 deg C, SmBO/sub 3/ inverted to the high NdBO/sub 3/ type polymorph. Below 1310 deg C, LuBO/sub 3/ formed the calcite-type structure. No polymorphism was observed in the eight intermediate borates. Indium borate showed only the calcite type structure. A discussion of the factors affecting polymorphism, such as radius ratio, density, and pressure, in addition to interpretation of infrared and structure data, may explain why the vaterite-type structure is more stable in the borates than in the carbonates. Unit cell dimensions are listed for indexed x-ray diffraction powder patterns, together with limited optical data. Published x-ray powder data for vaterite are compared. (auth)

• Research Organization: National Bureau of Standards, Washington, D.C.
• NSA Number: NSA-16-000162
• OSTI ID: 4837074
• Journal Information: Am. Mineralogist, Vol. Vol: 46; Other Information: Orig. Receipt Date: 31-DEC-62
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

CHEMISTRY
ARAGONITE
BORATES
CALCITE
CALCIUM CARBONATES
CARBONATES
CONFIGURATION
DENSITY
DIFFRACTION
DYSPROSIUM
ERBIUM
EUROPIUM
GADOLINIUM
HIGH TEMPERATURE
HOLMIUM
INDIUM
INFRARED RADIATION
IONS
LANTHANUM
LATTICES
LIGHT
LOW TEMPERATURE
LUTETIUM
MANGANESE
MELTING POINTS
MINERALS
NEODYMIUM
PRESSURE
RARE EARTHS
SAMARIUM
TEMPERATURE
THULIUM
VARIATIONS
VATERITE
X RADIATION
YTTERBIUM
YTTRIUM