Molecular Models and Calculations in Microscopic Theory of Order−Disorder Structural Phase Transitions:  Application to KH2PO4and Related Compounds

1996 ◽  
Vol 100 (15) ◽  
pp. 6258-6261 ◽  
Author(s):  
Alexandr A. Levin ◽  
Sergey P. Dolin
Keyword(s):  
Phase Transitions ◽  
Structural Phase ◽  
Microscopic Theory ◽  
Molecular Models ◽  
Structural Phase Transitions ◽  
Related Compounds

Tunability of τf in perovskites and related compounds

2002 ◽  
Vol 17 (8) ◽  
pp. 2033-2040 ◽  
Author(s):  
P. L. Wise ◽  
I. M. Reaney ◽  
W. E. Lee ◽  
D. M. Iddles ◽  
D. S. Cannell ◽  
...  
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Resonant Frequency ◽  
Room Temperature ◽  
Structural Phase ◽  
Structural Phase Transitions ◽  
Ionic Polarizability ◽  
Microwave Dielectrics ◽  
Related Compounds ◽  
Range Of Values

Tuning the temperature coefficient of resonant frequency (τf) in microwave dielectrics has been attributed to two main mechanisms: (i) dilution of the average ionic polarizability; (ii) the onset of an octahedral tilt transition above room temperature. The contributions of each mechanism have been isolated using ceramics in the Srn+1TinO3n+1, SrxCa1−x)3Ti2O7, and (SrxCa1−x)TiO3 series. In the Srn+1TinO3n+1 series, relative permittivity (εr) and τf are linearly proportional over a broad range of values, 100–37 and 800–140 ppm/°C, n = 4 and 1, respectively. No structural phase transitions occur on cooling from the prototype symmetry, and the mechanism of tuning is attributed solely to dilution of the average ionic polarizability as the SrO:SrTiO3 ratio increases. Exchanging Ca for Sr in the (SrxCa1−x)3Ti2O7 series resulted in an 80% reduction in the magnitude of τf from +320 to +50 ppm/°C but only 21% in permittivity (58 to 46). The effect was nonlinear and attributed primarily to the onset of a phase transition involving rotations of the octahedra on cooling. Superlattice reflections associated with the octahedral tilt transition have been identified.

Structural phase transitions in (TMTSF)2X and related compounds

1986 ◽  
Vol 13 (1-3) ◽  
pp. 63-69 ◽  
Author(s):  
S Ravy ◽  
R Moret ◽  
J.P Pouget ◽  
R Comes
Keyword(s):  
Phase Transitions ◽  
Structural Phase ◽  
Structural Phase Transitions ◽  
Related Compounds

ANOMALOUS DIFFUSION NEAR STRUCTURAL PHASE TRANSITIONS

1992 ◽  
Vol 06 (18) ◽  
pp. 1099-1103 ◽  
Author(s):  
W. K. HAN ◽  
S. C. YING ◽  
T. ALA-NISSILA
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Inhomogeneous Medium ◽  
Anomalous Diffusion ◽  
Structural Phase ◽  
Microscopic Theory ◽  
Central Peak ◽  
Structural Phase Transitions ◽  
Model Calculations ◽  
Physical Systems

Using a recently developed microscopic theory of diffusion for a particle coupled to an inhomogeneous medium, it has been shown that in the case of a structural phase transition with a diverging central peak, a diffusion anomaly occurs. We review results of model calculations demonstrating this anomaly on the W(100) surface, as well as discuss other physical systems where analogous phenomena may be observed.

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