Critical temperatures of superconductivity and neutron diffraction studies at 293 and at 10 K of molybdenum–iridium single crystals of A15 structure

1989 ◽  
Vol 22 (1) ◽  
pp. 23-25 ◽  
Author(s):  
R. Koksbang ◽  
S. E. Rasmussen ◽  
R. G. Hazell
Keyword(s):  
Phase Transition ◽  
Neutron Diffraction ◽  
Structural Phase ◽  
Cylindrical Sample ◽  
Inductive Method ◽  
Critical Temperatures ◽  
Lattice Constants ◽  
Main Transition ◽  
Ideal Composition ◽  
The Ideal

A crystal of dimensions 2.5 × 2.5 × 1.8 mm and of composition Mo3.25Ir was examined by neutron diffraction at 293 and 10 K. It has the A15 structure for which the space group is Pm3n and the ideal composition would be Mo3Ir. Least-squares refinements gave R(F) values of 0.013 and 0.017 for the 293 and the 10 K data, respectively. No structural phase transition was observed at 10 K. The lattice constants found were a = 4.967 (2) Å at 293 K and 4.958 (2) Å at 10 K. The transition temperature to superconductivity of the crystal was measured by an inductive method. An onset of superconductivity was found at 9.25 (5) K and a main transition at 9.10 (5) K. Another, approximately cylindrical, sample of volume 117 mm3 showed an onset at 8.6 (1) K and a main transition at 8.0 (1) K. About two thirds of this sample was a single-crystal.

Dynamic proton disorder and the II–I structural phase transition in (NH4)3H(SO4)2

2009 ◽  
Vol 65 (1) ◽  
pp. 36-44 ◽  
Author(s):  
Yoo Jung Sohn ◽  
Anja Loose ◽  
Michael Merz ◽  
Karine Sparta ◽  
Helmut Klapper ◽  
...  
Keyword(s):  
Phase Transition ◽  
Neutron Diffraction ◽  
Single Crystal ◽  
Powder Diffraction ◽  
Structural Phase ◽  
Local Symmetry ◽  
Crystal Structure Analysis ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Proton Disorder

X-ray powder diffraction, differential scanning calorimetry (DSC)/thermogravimetry (TG) and single-crystal neutron diffraction methods were used to investigate triammonium hydrogen disulfate (NH4)3H(SO4)2 (TAHS) in the temperature range between 293 and 493 K. The temperature-dependent X-ray powder diffraction measurements show a clear hysteresis of the I \leftrightarrow II phase transition of TAHS with transition temperatures of T up = 412.9 (1) K on heating and of T down = 402.6 (1) K on cooling. From the existence of hysteresis and from the jump-like changes of the lattice parameters, the I \leftrightarrow II phase transition of TAHS is considered to be first order. With DSC/TG measurements we confirmed that there is only one phase transition between 293 and 493 K. Through careful investigation on single crystals of TAHS using neutron diffraction, the correct space group (C2/c) of room-temperature TAHS-II phase was confirmed. Crystal structure analysis by single-crystal neutron diffraction showed a strongly elongated displacement ellipsoid of the proton which lies in the middle of the (SO4)H(SO4) dimer with \bar 1 local symmetry. The protons of the NH4 groups also show strongly enlarged anisotropic mean-square displacements. These findings are interpreted in terms of a characteristic proton disorder in the TAHS-II phase.

Neutron-diffraction study of a structural phase transition in the deuterated molecular ferromagnet Fe(dtc) 2 Cl

2002 ◽  
Vol 74 (0) ◽  
pp. s923-s925
Author(s):  
J. Campo ◽  
J. Luz�n ◽  
F. Palacio ◽  
G. DeFotis ◽  
J. Christophel ◽  
...  
Keyword(s):  
Phase Transition ◽  
Neutron Diffraction ◽  
Diffraction Study ◽  
Structural Phase Transition ◽  
Structural Phase ◽  
Neutron Diffraction Study

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.

Single-crystal neutron diffraction study of the structural phase transition in Ba0.95Ca0.05TiO3

1998 ◽  
Vol 10 (4) ◽  
pp. 899-899
Author(s):  
P U M Sastry ◽  
A Sequeira ◽  
H Rajagopal ◽  
B A Dasannacharya ◽  
S Balakumar ◽  
...  
Keyword(s):  
Phase Transition ◽  
Neutron Diffraction ◽  
Single Crystal ◽  
Diffraction Study ◽  
Structural Phase Transition ◽  
Structural Phase ◽  
Neutron Diffraction Study

Single-crystal neutron diffraction study of the structural phase transition in

1996 ◽  
Vol 8 (16) ◽  
pp. 2905-2913 ◽  
Author(s):  
P U M Sastry ◽  
A Sequeira ◽  
H Rajagopal ◽  
B A Dasannacharya ◽  
S Balakumar ◽  
...  
Keyword(s):  
Phase Transition ◽  
Neutron Diffraction ◽  
Single Crystal ◽  
Diffraction Study ◽  
Structural Phase Transition ◽  
Structural Phase ◽  
Neutron Diffraction Study
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