Phase Transitions in MnO and FeO at Low Temperatures: A Neutron Powder Diffraction Study.

AbstractThe structure of a synthetic sample of analcime has been determined as a function of temperature between 30–300 K by high-resolution neutron powder diffraction. Although there are some reports of samples of analcime having non-cubic structures, the sample in our experiments remained cubic (space group la3d), and hence disordered, down to low temperatures. The absence of phase transitions involving ordering of the orientations of the water molecules, ordering of the sodium positions, or a displacive instability as in leucite and related materials, is discussed. We speculate that part of the reason for the absence of ordering of the water molecules or sodium cations is associated with the Al/Si disorder, which cannot order at low temperatures. We also discuss the likely distribution of the orientations of the water molecules at low temperatures, and propose that the water diads lie close to any of the crystal diads with the H-H Vectors lying close to the triads.

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High-resolution neutron powder diffraction study on the phase transitions in BaPbO3

Journal of Solid State Chemistry ◽

10.1016/j.jssc.2007.03.009 ◽

2007 ◽

Vol 180 (5) ◽

pp. 1559-1565 ◽

Cited By ~ 12

Author(s):

W.T. Fu ◽

D. Visser ◽

K.S. Knight ◽

D.J.W. IJdo

Keyword(s):

Phase Transitions ◽

High Resolution ◽

Diffraction Study ◽

Powder Diffraction ◽

Neutron Powder Diffraction

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Magnetic structures and phase transitions of Nickel-Bromine boracite Ni3B7O13Br. a neutron powder diffraction study

Ferroelectrics ◽

10.1080/00150199308008529 ◽

1993 ◽

Vol 146 (1) ◽

pp. 81-97 ◽

Cited By ~ 9

Author(s):

S. Y. Mao ◽

F. Kubel ◽

H. Schmid ◽

P. Schobinger ◽

P. Fischer

Keyword(s):

Phase Transitions ◽

Diffraction Study ◽

Powder Diffraction ◽

Neutron Powder Diffraction ◽

Magnetic Structures

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Neutron powder diffraction study of the phase transitions in deuterated methylammonium lead iodide

Journal of Physics Condensed Matter ◽

10.1088/1361-648x/ac4aa9 ◽

2022 ◽

Author(s):

Jiaxun Liu ◽

Juan Du ◽

Anthony E Phillips ◽

Peter B Wyatt ◽

David A Keen ◽

...

Keyword(s):

Phase Transitions ◽

Diffraction Study ◽

Powder Diffraction ◽

Landau Theory ◽

Orthorhombic Phase ◽

Neutron Powder Diffraction ◽

Temperature Phase ◽

Lead Iodide ◽

Lower Temperature ◽

Methylammonium Lead Iodide

Abstract We report the results of a neutron powder diffraction study of the phase transitions in deuterated methylammonium lead iodide, with a focus on the system of orientational distortions of the framework of PbI6 octahedra. The results are analysed in terms of symmetry-adapted lattice strains and normal mode distortions. The higher-temperature cubic–tetragonal phase transition at 327 K is weakly discontinuous and nearly tricritical. The variations of rotation angles and spontaneous strains with temperature are consistent with a standard Landau theory treatment. The lower-temperature transition to the orthorhombic phase at 165 K is discontinuous, with two systems of octahedral rotations and internal distortions that together can be described by five order parameters of different symmetry. In this paper we quantify the various symmetry breaking distortions and their variation with temperature, together with their relationship to the spontaneous strains, within the formalism of Landau theory. A number of curious results in the low-temperature phase are identified, particularly regarding distortion amplitudes that decrease rather than increase with lowering temperature.

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