Effects Of Size Disorder Research Articles

Design, synthesis, and influencing factors of medium-/high-entropy Y2(ZrTiGeHfSnSi)2O7 with a pyrochlore structure

A set of medium-/high-entropy pyrochlore oxides (M-HEPOs) with different compositions were designed and synthesized. The phase compositions of the prepared materials were determined through X-ray diffraction and Raman spectroscopy. Among the 24 designed samples, two high-entropy and six medium-entropy samples formed single-phase pyrochlore materials, two medium-entropy samples formed dual-phase pyrochlore materials, and the others formed multiphase materials dominated by the pyrochlore phase. The factors affecting the formation of single-phase pyrochlore structure were studied. The results revealed that size disorder is a major element determining the formation of single-phase pyrochlore, whereas mixing entropy has minimal effect. It is anticipated that this study will provide significant insights into the effects of size disorder and mixing entropy on the formation of M-HEPOs.

Effect of size disorder on the structure and magnetic properties of La0.3R0.2Sr0.5Ti0.5Fe0.5O3 (R = La, Nd, Gd, and Dy) compounds

Successful preparation of perovskite oxides of chemical formula La0.3R0.2Sr0.5Ti0.5Fe0.5O3 (R = La, Nd, Gd, and Dy) has been achieved by citrate-gel precursor method, and their structures were determined using powder X-ray diffraction (XRD). The Rietveld analysis of the XRD data showed that all the samples have anti-site disorder. Anti-site disorder has not been seen to alter the symmetry of crystal structure but leads to tilt of the Fe3+ neighbouring octahedral which by its role gives rise to canted anti-ferromagnetism as a result of anti-parallel misalignment of the magnetic moments of the Fe3+ ions.

Effect of size disorder on the optical transport in chains of coupled microspherical resonators

We investigate statistical properties of collective optical excitations in disordered chains of microspheres using transfer-matrix method based on nearest-neighbors approximation. Radiative losses together with transmission and reflection coefficients of optical excitations are studied numerically. We found that for the macroscopically long chain, the transmission coefficient demonstrates properties typical for a one dimensional strongly localized system: log-normal distribution with parameters obeying standard scaling relation. At the same time, we show that the distribution function of the radiative losses behaves very differently from other lossy optical systems. We also studied statistical properties of the optical transport in short chains of resonators and demonstrated that even small disorder results in significant drop of transmission coefficient acompanied by strong enhancement of the radiative losses.

Wave propagation in two-dimensional disordered piezoelectric phononic crystals

The wave propagation is studied in two-dimensional disordered piezoelectric phononic crystals using the finite-difference time-domain (FDTD) method. For different cases of disorder, the transmission coefficients are calculated. The influences of disorders on band gaps are investigated. The results show that the disorder in the piezoelectric phononic crystals has more significant influences on the band gap in the low frequency regions than in the high frequency ones. The relation between the width of band gap and the direction of position disorder is also discussed. When the position disorder is along the direction perpendicular to the wave transmission, the piezoelectric phononic crystals have wider band gaps at low frequency regions than the case of position disorder being along the wave transmission direction. It can also be found that the effect of size disorder on band gaps is analogous to that of location disorder. When the perturbation coefficient is big, it has more pronounced effects on the pass bands in the piezoelectric phononic crystals with both size and location disorders than in the piezoelectric phononic crystals with single disorder. In higher frequency regions the piezoelectric effect reduces the transmission coefficients. But for larger disorder degree, the effects of the piezoelectricity will be reduced.

Effect of size disorder on the magnetic and transport properties of the (LaR) 0.55(CaSr) 0.45MnO 3 (R=Nd, Sm & Tb) compounds

Electrical resistivity, magnetization and magnetoresistance (MR) measurements have been performed on ABO 3-type (LaR) 0.55(CaSr) 0.45MnO 3 (R=Nd, Sm and Tb) compounds, in which A-site size disorder varies but tolerance factor remains constant. The insulator–metal (I–M) transition temperature ( T p) and the Curie temperature ( T C) of these compounds decrease from ∼170 K for R=Nd to ∼120 K for R= Tb, which is consistent with increasing size disorder. All the samples exhibit maximum in MR at T p and an MR of 70–80% at 5 K. The reduced T p and T C and enhanced MR in these compounds vis-`a-vis the T p and T C of ∼230 K of the standard La 0.55Ca 0.45MnO 3 compound, may be attributed to the local structural distortions induced by enhanced A-site size-disorder.

Empirical versus ab initio atomic radii for melting theory of disordered alloys

It has been suggested that the failure of Lindemann theory to predict the melting temperature of alkali metal alloys results from the neglect of size disorder. When the effects of size disorder are added to the theory in a similar way to vibrational (thermal) disorder and atomic radii derived from experiment are used as input, one can accurately predict alloy melting temperatures. In contrast, when this approach is used with atomic radii derived from ab initio pseudopotentials, it fails to recreate the experimental melting curves. Although the added size disorder term is itself explicitly independent of temperature, a functional temperature dependence of the radii is necessary to reproduce accurately the melting data.