M. De

Electronic structure and optical properties of neodymium monopnictides

Abstract The electronic structure and optical properties of neodymium monopnictides have been investigated. The linear muffin-tin orbital method in the atomic sphere approximation and the local density approximation to exchange and correlation in density functional theory has been used. The p–f mixing increases while f-band width decreases on going down the pnictogen column due to the increase in pnictogen size. The density of states at the Fermi energy increases on going from NdP to NdSb. The joint density of states and partial oscillator strength have been calculated. The optical conductivity at higher energy increases with the increase of pnictogen atomic number due to the increase in p→d and f→d oscillator strengths.

An x‐ray diffraction study on the microstructures of cold‐worked fcc Cu‐Ni‐Zn alloys

The state of cold work in the ternary Cu‐Ni‐Zn alloy system (fcc) has been investigated by x‐ray diffraction from a detailed analysis of the peak shift, peak asymmetry, and peak broadening. Cold working in the system produces an appreciable amount of intrinsic stacking faults which play the most important role in peak broadening as well as in shifting the positions of the diffraction profiles. For the observed peak shift, the other contributing factors (namely, lattice‐parameter change and long‐range residual stresses) are relatively small. Asymmetry in the profiles is due to the presence of a very small amount of extrinsic stacking fault, and deformation twins have been found to be totally absent. The estimations of domain size, rms strains, and the dislocation density in the alloys have been made from the peak‐broadening analysis, and the stacking‐fault energy for pure copper has also been evaluated and has been found to be comparable. The presence of the transitional solute Ni from 1 to 15 wt% has a ve...

Lattice imperfection studies in polycrystalline materials by x-ray diffraction line-profile analysis

This review concerns our recent investigations with a series of binary fcc Ag- and Cu-base alloys (viz Ag-Ga, Ag-Ge, Ag-Al and Cu-Ga, Cu-Ge) from detailed analyses of x-ray diffraction line profiles, the importance of which has been briefly summarized. The theoretical formulations of the Warren-Averbach’s method of Fourier analysis of peak-shapes along with the methods of peak-shift and peak-asymmetry have been outlined. A preview on the significant studies carried out earlier with Ag- and Cu-base (fcc) binary alloys has been made in short. A detailed analyses on the recorded profiles in the present considerations revealed, in general, quantitative estimates of several microstructural parameters characterising the deformed state of the materials namely, propensity of stacking faults (intrinsic, extrinsic and twin faults), rms microstrains, coherent domain sizes, long-range residual stresses, lattice parameter changes, dislocation density and stacking fault energy. The results indicate a general trend of increase in the concentrations of stacking faults, primarily, of intrinsic character, with increase in solute concentrations; which are solely responsible for the observed peak-shifts as well as domain size broadening. Small asymmetry in the profiles is due to the presence of extrinsic stacking faults, relatively less in magnitude compared to the intrinsic ones while the deformation twin faults are almost absent—an observation with significance. The dislocation density, quite appreciable in magnitude, has been evaluated from the anisotropic values of the coherent domain sizes and rms microstrains. The stacking fault energies of pure Ag and Cu, an important parameter have also been estimated and compared with those obtained from electron microscopy. Annealing experiments with a Ag-5·8% Al alloy, aluminium being a precipitating solute, do not reveal any detectable evidence of solute segregation at the stacking faults. The occurrence of stacking faults in the alloy systems has been correlated with a number of physical factors involving solvent-solute types.

The thermal expansion and temperature dependence of tetragonal distortion in ZnSiAs2 determined by an X-ray diffraction method

Abstract The thermal expansion of ZnSiAs2, a II-IV-Vb chalcopyrite compound, was measured at temperatures up to 600 °C using X-ray techniques. The coefficient αc was smaller than the coefficient αa, and this anisotropy is explained in terms of the thermal expansions of the two types of II-V and IV-V bonds. General trends in the temperature dependence of the tetragonal distortion of these compounds indicated by the experimental observations are discussed.

On the occurrence of extrinsic stacking faults in some copper-base and silver-base alloys

The earlier X-ray data of stacking-fault probabilities in some cold-worked Cu-base and Ag-base alloys have been reanalysed to detect the presence of extrinsic faults. Results indicate that these are present in the alloys having higher solute content. The probability of their occurrence increases with the increase of the valency of the solutes and with the increase of intrinsic faults and decrease of twin faults. However, in certain cases, the measured twin-fault probabilities not only decrease, but become unreasonably large and negative. The observations are in accordance with recent findings on the occurrence of extrinsic faults in cold-worked face-centred cubic alloys.

Electronic structure and optical properties of praseodymium monopnictides

Abstract The electronic structure and optical properties of praseodymium monopnictides have been investigated. The linear muffintin orbital method in the atomic sphere approximation and the local density approximation to exchange and correlation in density functional theory has been used. The p bands of pnictogen move towards higher energy on going down the pnictogen column. The density of states at the Fermi energy increases on going from PrP to PrSb. The calculated optical conductivity is compared with the available experimental data. The optical conductivity increases with the increase of pnictogen atomic number.

An x‐ray diffraction line profile analysis on the microstructure of cold‐worked face‐centered‐cubic Cu‐Mn‐Si alloys: Effects of Mn and Si as solutes

In continuation of our earlier investigations on the microstructures of cold‐worked Cu‐(Sn,Ni,Mn)‐Zn ternary alloys by x‐ray diffraction line profile analysis [J. Appl. Phys. 54, 6652 (1983); ibid. 48, 3560 (1977); ibid. 56, 1213 (1984)] the present work with Cu‐Mn‐Si alloy system in the fcc phase has been undertaken to elucidate the effects of Mn and Si, when present together, on the cold‐worked substructure of this system. From detailed analyses of peak shift, peak asymmetry, and Fourier line shapes, quantitative estimates of the related microstructural parameters, namely, intrinsic (α’), extrinsic (α‘), and twin fault (β) probabilities, domain sizes, rms strain, dislocation density, and stacking fault energy (for pure Cu), have been made. The results indicate, as in the earlier cases, increased presence of intrinsic stacking faults (α’)—primarily responsible for the observed peak shift and domain size broadening with relatively small presence of extrinsic faults (α‘) and complete absence or very small ...

X-ray measurements of stacking faults in copper–antimony alloys

The line profiles from cold-worked copper-base alloys containing pentavalent solute antimony in the primary solid solution range have been recorded by a Geiger counter X-ray diffractometer. The deformation fault probability α and the twin fault probability β have been obtained from peak shift and peak asymmetry measurements respectively. A roughly parabolic variation of α with increasing solute content has been observed. However, the increase of α with the increase of solute valency for fixed electron concentration per atom is not clearly established. The twin fault probability βalso increases in a similar way as observed in other copper-base alloys.

X-Ray Diffraction Studies of Cold-Worked Copper-Antimony Alloys

The deformation stacking fault probability α and twin stacking fault probability β in cold-worked copper-antimony alloys have been obtained from peak shift and peak asymmetry measurements of the X-ray line profiles, and the fault parameter α has been found to increase in a roughly parabolic manner with increasing solute concentration but the increase with increasing solute valency for fixed e / a is not clearly established. The anisotropic values of the particle size [ D e ] h k l and r. m. s. strain [ ] h k l 1/2 have been evaluated using both Fourier analysis of line shapes and integral breadth methods, and the lattice parameters have been found to vary considerably with increasing solute content. The values of the compound fault probability (1.5α+β) obtained from two independent methods are in fair agreement and the role of stacking faults in the particle size broadening is clearly seen. Particle sizes and strain values are also utilized for an estimation of dislocation density ρ in the cold-wor...

Magnetic and magneto-optical properties of NdX (X = P, As, Sb, Bi)

The magnetic and magneto-optical properties of NdX (X = P, As, Sb, Bi) in the ferromagnetic phase derived from an electronic structure calculation have been presented. The calculation is performed using the local spin-density approximation (LSDA) and also the LSDA corrected with the Coulomb interaction U (the LSDA+U). The LSDA+U density of states at the Fermi level is small and the carrier density is also low. The magnetism in NdP, NdAs and NdSb is found to be dominated by a large orbital contribution coupled antiparallel to the spin moment. The anisotropic mixing between the p states of X and the f states of Nd provides the large off-diagonal optical conductivity.