A qualitative X-ray diffraction study of the 205°K and 151°K phase transformations in praseodymium aluminate (PrAlO<sub>3</sub>)

Burbank, R. D.

doi:10.1107/s0021889870005794

Cited by 63 publications

(32 citation statements)

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“…3. Burbank (1970); there is an arithmetical inconsistency in the paper, and Dr Burbank has confirmed (personal communication) that the correct value of should be 6"5% 4. Darlington & Megaw (1973).…”

Section: Tilt Angle and A-cation Sizementioning

confidence: 99%

Geometrical and structural relations in the rhombohedral perovskites

Megaw¹,

Darlington²

1975

Acta Cryst A

332

209

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The rhombohedral perovskites are of interest in lattice dynamics (e.g. LaA103, PrA103) and for their ferroelectric properties (e.g. LiNbO3, PbZr/TiO3). In this paper, data scattered through the literature are correlated, with correction of some misleading mistakes of calculation. Geometrical descriptions are put in a form allowing comparisons. The structures, classified by their space groups, are described in terms of four structural parameters, the octahedron tilt co, octahedron distortion d, and A-and B-cation displacements s and t, together with an elongation or flattening ~ of the octahedron, deducible with the help of co from the interaxial angle a,h. Attention is drawn to the variety of physical causes underlying these departures from ideal perovskite. In the R-3e structures a correlation not previously noted in the literature is found between the tilt angle co and a flattening of the octahedron, and some tentative suggestions are made as to its cause. In the R3m and R3e structures, a lack of general correlation between B-cation displacement and the other parameters is noted, in contradiction to earlier reports.

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Section: Tilt Angle and A-cation Sizementioning

confidence: 99%

Geometrical and structural relations in the rhombohedral perovskites

Megaw¹,

Darlington²

1975

Acta Cryst A

332

209

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“…No known examples SrZrO 3 (973-1103 K) NaNbO 3 (793-848 K) NaTaO 3 (803-873 K) NHaMnCI 3 (128 K) PrAIO 3 ( < 135 K) Marezio, Dernier, Chenevas & Joubert (1973) Chenevas, Joubert, Marezio & Bochu (1975 Ahtee, Glazer & Megaw (1972) Ahtee & Darlington (1980) Tornero, Cano, Fayos & Martinez-Ripoll (1978) Burbank (1970) …”

mentioning

confidence: 99%

Octahedral Tilting in Perovskites. II. Structure Stabilizing Forces

Woodward¹

1997

Acta Crystallogr B Struct Sci

625

480

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The 23 Glazer tilt systems describing octahedral tilting in perovskites have been investigated. The various tilt systems have been compared in terms of their A-cation coordination and it is shown that those tilt systems in which all the A-cation sites remain crystallographically equivalent are strongly favored, when all the A sites are occupied by the same ion. Calculations based on both ionic and covalent models have been performed to compare the seven equivalent A-site tilt systems. Both methods predict that when the tilt angles become large, the orthorhombic a+b-b -tilt system will result in the lowest energy structure. This tilt system gives the lowest energy structure because it maximizes the number of short A---O interactions. The rhombohedral a-a-a-tilt system gives a structure with a slightly lower Madelung energy, but increased ion-ion repulsions destabilize this structure as the tilt angles increase. Consequently, it is stabilized by highly charged A cations and small to moderate tilt angles. The ideal cubic a°a°a° tilt system is only observed when stabilized by oversized A cations and/or M---O 7r-bonding. Tilt systems with nonequivalent A-site environments are observed when at least two A cations with different sizes and/or bonding preferences are present. In these compounds the ratio of large-to-small cations dictates the most stable tilt system.

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“…However, there seems to be no a priori reason for an AB03 perovskite to show a double cubic cell instead of the more usual ones: simple cubic as SrTiOs, orthorhombic as GdFeOs or even monoclinic as PrA103 (Burbank, 1970).…”

Section: Introductionmentioning

confidence: 99%