Pressure induced structural phase transition in IB transition metal nitrides compounds

2015 ◽  
Author(s):  
Shubhangi Soni ◽  
Netram Kaurav ◽  
A. Jain ◽  
S. Shah ◽  
K. K. Choudhary
Keyword(s):  
Phase Transition ◽  
Transition Metal ◽  
Structural Phase Transition ◽  
Structural Phase ◽  
Metal Nitrides ◽  
Transition Metal Nitrides

A structural phase transition in NaTaOGeO4 and its relation to phase transitions in titanite

2007 ◽  
Vol 63 (4) ◽  
pp. 545-550 ◽  
Author(s):  
Thomas Malcherek
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Transition Metal ◽  
Structural Phase Transition ◽  
Order Parameter ◽  
Diffuse Scattering ◽  
Structural Phase ◽  
Group Symmetry ◽  
Critical Temperatures ◽  
Symmetry Properties

A structural phase transition from space-group symmetry P21/c to C2/c is reported for NaTaOGeO4 (NTGO). The critical temperature has been located at T c = 116 K, based on the appearance of sharp diffraction maxima at positions h + k = 2n + 1 of reciprocal space on cooling below this temperature. Strongly anisotropic diffuse scattering in sheets normal to [001] is observable for T > T c and persists up to ambient temperature. Similarities to phase transitions observed in other compounds of the titanite structure type are discussed. The symmetry properties of these phase transitions are reassessed on the basis of the structural data available. The primary order parameter is identified with the displacement of the transition metal cation M (M = Ta in NTGO) away from the centre of symmetry that it nominally occupies in the paraphase. The order parameter transforms as the Y_{2}^{-} representation. The anisotropic diffuse scattering is attributed to the one-dimensional correlation of local M displacements parallel to the direction of chains of trans-corner-sharing MO6 octahedra. The critical temperatures of the isomorphous phase transitions in various titanite-type compounds depend linearly on the squared transition-metal displacement measured in the ordered P21/c phase.

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