scholarly journals Temperature‐dependent Raman study of ammonium perchlorate single crystals: The orientational dynamics of the NH+4ions and phase transitions

1986 ◽  
Vol 84 (12) ◽  
pp. 7018-7027 ◽  
Author(s):  
T. Chakraborty ◽  
S. S. Khatri ◽  
A. L. Verma
Keyword(s):  
Phase Transitions ◽  
Single Crystals ◽  
Ammonium Perchlorate ◽  
Temperature Dependent ◽  
Raman Study ◽  
Orientational Dynamics

scholarly journals Temperature-Dependent Evolution of Raman Spectra of Methylammonium Lead Halide Perovskites, CH3NH3PbX3 (X = I, Br)

Molecules ◽  
2019 ◽  
Vol 24 (3) ◽  
pp. 626 ◽  
Author(s):  
Kousuke Nakada ◽  
Yuki Matsumoto ◽  
Yukihiro Shimoi ◽  
Koji Yamada ◽  
Yukio Furukawa
Keyword(s):  
Phase Transitions ◽  
Temperature Dependence ◽  
Temperature Dependent ◽  
High Power Conversion Efficiency ◽  
Perovskite Materials ◽  
Hybrid Perovskite ◽  
Temperature Ranges ◽  
Raman Study ◽  
Halide Perovskites ◽  
Motional Narrowing

We present a Raman study on the phase transitions of organic/inorganic hybrid perovskite materials, CH3NH3PbX3 (X = I, Br), which are used as solar cells with high power conversion efficiency. The temperature dependence of the Raman bands of CH3NH3PbX3 (X = I, Br) was measured in the temperature ranges of 290 to 100 K for CH3NH3PbBr3 and 340 to 110 K for CH3NH3PbI3. Broad ν1 bands at ~326 cm−1 for MAPbBr3 and at ~240 cm−1 for MAPbI3 were assigned to the MA–PbX3 cage vibrations. These bands exhibited anomalous temperature dependence, which was attributable to motional narrowing originating from fast changes between the orientational states of CH3NH3+ in the cage. Phase transitions were characterized by changes in the bandwidths and peak positions of the MA–cage vibration and some bands associated with the NH3+ group.

A Thermo-Magneto-Mechanical Free Energy Model for NiMnGa Single Crystals

2007 ◽  
Vol 1050 ◽  
Author(s):  
Phillip Morrison ◽  
Stefan Seelecke ◽  
Manfred Kohl ◽  
Berthold Krevet
Keyword(s):  
Free Energy ◽  
Phase Transitions ◽  
Single Crystals ◽  
Energy Landscape ◽  
Stable States ◽  
Temperature Dependent ◽  
One Dimensional ◽  
Rate Dependent ◽  
Energy Equations ◽  
Increasing Temperature

AbstractThe paper extends the authors' recent model for one-dimensional rate-dependent magneto-mechanical behavior of NiMnGa single crystals to account for temperature-dependent effects including austenite/martensite and ferro-/paramagnetic phase transitions. The magneto-mechanical model is based on the Helmholtz free energy landscape constructed for a meso-scale lattice element with strain and magnetization as order parameters. This two-dimensional energy landscape includes three paraboloidal wells representing the two easy-axis and one hard-axis martensite variants relevant for the structurally one-dimensional case. Phase transformations resulting from applied stresses and magnetic fields follow from a system of evolution laws based on the Gibbs free energy equations and the theory of thermally activated processes, which in the low-thermal-activation limit appropriately reproduce the athermal transformation behavior observed in these materials. The phase fractions subsequently determine the macroscopic strain and magnetization of a sample of NiMnGa by means of a standard averaging procedure. To account for the first-order phase transitions to austenite, additional temperature-dependent wells representing the stable states of austenitic NiMnGa are introduced into the Helmholtz energy landscape. The transition from ferromagnetic to paramagnetic states is modeled as a second order transformation based on the gradual degeneration of the ferromagnetic wells with increasing temperature.

Laser Raman study of phase transitions in [N(CH3)4]2COCl4 single crystals

1987 ◽  
Vol 18 (6) ◽  
pp. 429-434 ◽  
Author(s):  
R. P. Rathore ◽  
S. S. Khatri ◽  
T. Chakraborty
Keyword(s):  
Phase Transitions ◽  
Single Crystals ◽  
Laser Raman ◽  
Raman Study

scholarly journals Magnetic phase transitions in Eu( Co1−xNix)2−yAs2 single crystals

2020 ◽  
Vol 4 (8) ◽  
Author(s):  
N. S. Sangeetha ◽  
Santanu Pakhira ◽  
D. H. Ryan ◽  
V. Smetana ◽  
A.-V. Mudring ◽  
...  
Keyword(s):  
Phase Transitions ◽  
Single Crystals ◽  
Magnetic Phase ◽  
Magnetic Phase Transitions
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