Quantum Fluctuations in Granular Superconductors

1990 ◽  
Vol 195 ◽  
Author(s):  
R.S. Fishman
Keyword(s):  
Order Parameter ◽  
Short Range ◽  
Short Range Order ◽  
Quantum Fluctuations ◽  
Thermal Fluctuations ◽  
Range Order ◽  
Range Order Parameter ◽  
Long Range Order ◽  
Phase Fluctuations ◽  
Granular Superconductors

ABSTRACTA 1/z expansion is used to study the coupling of phase fluctuations in an array of superconducting grains. By lowering Tc. and increasing the critical grain diameter αc,fluctuations suppress the long-range order in the material. When the temperature T is of order U = e2/C, where C is the grain capacitance, peaks appear in the fluctuation corrections to both the specific heat and the short-range order parameter. These peaks are induced by the coupling between thermal fluctuations of the charge and quantum fluctuations of the phase on neighboring grains.

Pb()O3-type Perovskites: Part I. Pair-correlation Theory of Order-disorder Phase Transition

1997 ◽  
Vol 12 (8) ◽  
pp. 2117-2126 ◽  
Author(s):  
Hyun M. Jang ◽  
Su-Chan Kim
Keyword(s):  
Long Range ◽  
Order Parameter ◽  
Short Range ◽  
Short Range Order ◽  
Pair Correlation ◽  
Range Order ◽  
Statistical Thermodynamic ◽  
Range Order Parameter ◽  
Long Range Order ◽  
Short Range Order Parameter

The limitation of the long-range order parameter and the necessity of the short-range order parameter for the thermodynamic description of Pb()O3-type perovskites are discussed. Based on the discussion, a statistical thermodynamic model that takes into account the configuration of the neighboring B-site ions (B′ and B″ cations) was developed. A pair-correlation approximation was used in the calculation of the configurational entropy and the long-range coulombic interaction energy between the nearest B-site ions. The theoretical calculations using Pb(Sc1/2Ta1/2)O3 (PST) and Pb(Sc1/2Nb1/2)O3 (PSN) systems indicate that the short-range order parameter persists over a wide range of temperatures examined (0–1800 K) and that there possibly occur consecutive long-range order-disorder transitions in the configuration of B-site cations. The possibility of the existence of short-range ordering above the long-range order-disorder transition temperature was also examined using the annealed PSN specimen as a typical example of Pb()O3-type perovskites.

A New Parametric Method for the Analysis of Ordering Configurations in Binary Alloys

1992 ◽  
Vol 278 ◽  
Author(s):  
T.W. Staley ◽  
R.J. Matyi
Keyword(s):  
Monte Carlo ◽  
Order Parameter ◽  
Short Range ◽  
Short Range Order ◽  
Parametric Method ◽  
Range Order ◽  
Range Order Parameter ◽  
Long Range Order ◽  
Geometric Variation ◽  
Alloy Systems

AbstractIn ordering alloy systems, the overall long-range order parameter does not distinguish the degree to which the component structures are delocalized for different configurations of equal randomness. We define a new parameter, which is sensitive to such differences, by considering the short-range order parameters as a set of statistical moments for geometric variation in the crystal. A computer model has been developed which uses this parameter to analyze finite alloy systems for configurational preferences by a Monte Carlo method. Initial studies have established the parametric range as a function of LRO and nonstoichiometry. Qualitative results correspond well to predictions for ideal systems.

Surface Ordering of MBE Grown 001 Ga1−xAlxAs- A Theoretical Study

1991 ◽  
Vol 241 ◽  
Author(s):  
Rita Trivedi ◽  
R. Venkatasubramanian
Keyword(s):  
Order Parameter ◽  
Short Range ◽  
Short Range Order ◽  
Theoretical Study ◽  
Flux Ratio ◽  
Range Order ◽  
Range Order Parameter ◽  
Mbe Growth ◽  
Short Range Order Parameter ◽  
Surface Migration

ABSTRACTThe kinetics of MBE growth of Ga1-x.,Alx,As is studied theoretically using the stochastic model of MBE growth based on the master equation approach and the random distribution approximation. The surface ordering phenomenon during the 001 growth of Ga0.5Al0.5 As is investigated as a function of the growth conditions. The atom pair interaction energy parameters for various surface configurations were obtained from the first principle calculations. The other model parameters needed in the description of the kinetic processes are obtained from the available experimental data. The ordering kinetics is studied as a function of fluxes, flux ratio and growth temperature. The degree of ordering is estimated in terms of the short range order parameter. The short range order parameter increases with temperature till 650°K and 750°K for cation to anion flux ratios 2 : 1 and 1 : 5, respectively. Beyond this critical temperature, the short range order parameter decreases. This critical temperature is identified as the kinetic order-disorder temperature. The order-disorder phenomenon observed in this theoretical study is explained in terms of the dependence of the surface migration rate of the cations on the growth temperature. The dependence on the order-disorder temperature on the flux ratio is attributed to decreased surface migration for larger flux ratios.

Pb()O3-type Perovskites: Part II. Short-range Order Parameter as a Criterion of the Distinction Between Relaxor and Normal Ferroelectrics

1997 ◽  
Vol 12 (8) ◽  
pp. 2127-2133 ◽  
Author(s):  
Su-Chan Kim ◽  
Hyun M. Jang
Keyword(s):  
Coherence Length ◽  
Order Parameter ◽  
Short Range ◽  
Short Range Order ◽  
Order Parameters ◽  
Range Order ◽  
Relaxor Behavior ◽  
Range Order Parameter ◽  
Short Range Order Parameter ◽  
Short Range Ordering

A classification scheme of Pb()O3-type perovskites with respect to the B-site order parameters was proposed based on the theoretical calculation of the short-range order parameter (σ) using the pair-correlation model. The calculated order parameters predict that a Pb()O3-type perovskite without any charge difference between B′ and B″ cations [e.g., Pb(Zr1/2Ti1/2)O3 (PZT)] is represented by a completely disordered state with the absence of a finite coherence length. On the other hand, a Pb()O3-type perovskite system having different ionic charges is characterized either by the short-range ordering with a nanoscale coherence length or by the macroscopic long-range ordering, depending on the magnitude of ionic charge difference between B′ and B″ ions. The normal ferroelectricity in Pb()O3-type complex perovskites was then correlated either with a completely disordered state (σ = 0) or with a perfectly ordered state (σ = 0), whereas the relaxor behavior was attributed to the nanoscale short-range ordering (0 < σ < 1) in the configuration of the B-site cations.

scholarly journals Anomaly in energetic and structural properties of MgSn liquid alloys

BIBECHANA ◽  
1970 ◽  
Vol 7 ◽  
pp. 33-38
Author(s):  
A Kumar ◽  
IS Jha ◽  
BP Singh
Keyword(s):  
Lattice Model ◽  
Order Parameter ◽  
Short Range ◽  
Short Range Order ◽  
Wave Length ◽  
Range Order ◽  
Heat Of Mixing ◽  
Range Order Parameter ◽  
Molten State ◽  
Short Range Order Parameter

The observed asymmetry in the properties of mixing of MgSn alloy in molten state is successfully explained on basis of the quasi-lattice model. It has been utilized to determine the free energy of mixing, entropy of mixing, heat of mixing, the concentration- concentration structure factor in long wave-length limit [Scc(0)] and the Warren Cowley short range order parameter (α1) of MgSn alloy in molten state at 1073 K. The analysis suggests that heterocordiantion leading to the formation of chemical complex Mg2Sn is likely to exist in the melt but is of a weakly interacting in nature. The interaction energies between the species of the melt are found to depend considerably on temperature and the alloy is more ordered towards Mg rich region Keywords: Quasi-lattice model; Binary alloys; Short range order parameter; Asymmetry DOI: 10.3126/bibechana.v7i0.4042BIBECHANA 7 (2011) 33-38

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