d band widths in CdMg and CuZn alloys

The binary alloys Cd₃Mg, Mg₃Cd and ZnCu 20% at. have been studied using X-ray photoelectron spectroscopy (XPS). The Cd 4d bandwidths are reduceThe Cu 3d band in ZnCu 20% is found to have a width of 1.1 ± 0.1 eV and binding energy of 3.5 ± 0.1 eV. The results are discussed.     

Density-of-states in the valence band of some alloys on a gold base

The present work deals with the investigation of X-ray photoelectronic spectra of the alloys PtAu, CuAu, NiAu. It is shown that d-states of the components preserve their individualities in these alloys to a marked degree.     

Relocalization of Ce 5d electrons from host conduction band

Single crystal fibers of Ce³⁺ doped SrAl₂O₄ and CaAl₄O₇ were prepared through the laser heated pedestal growth method. Sites dependent Ce³⁺ emissions were found at 385 nm (427 nm) and 420 nm (325 nm) in SrAl₂O₄ and CaAl₄O₇ hosts, respectively. The Ce³⁺ emissions at 385 nm and 420 nm in the two hosts exhibited strong afterglows. They could persist for more than 10 h. The long persistence and sites dependence of Ce³⁺ emissions were originated from charge compensation of doping Ce³⁺ into divalent cation sites. The lifetimes of Ce³⁺ emissions in both hosts were found to depend on the laser excitation wavelengths. With 266 nm laser excitation, Ce³⁺ 5d electrons were delocalized into the host's conduction band, resulting in a prolonged decay time. The 355 nm laser excitation did not delocalize the 5d electrons and hence the measured lifetimes were the intrinsic Ce³⁺ emission lifetimes that were 17 and 35.5 ns in SrAl₂O₄ and CaAl₄O₇ hosts, respectively. The prolonged Ce³⁺ emission lifetime on 266 nm laser excitation was because of the relocalization of the 5d electrons from the host conduction band. The lifetimes of Ce³⁺ 5d electrons within the conduction band were found to be 34 and 44 ns in SrAl₂O₄ and CaAl₄O₇ hosts, respectively.     

The Invar behaviour of iron-nickel-platinum alloys

The ordering temperatures of alloys in the quasi-binary section Fe₃(Ni_xPt_1−x) have been determined experimentally, and are found to be consistent with theoretical predictions. Lattice constants and expansion coefficients vary smothly between Fe_0.75Ni_0.25 and Fe_0.75Pt_0.25 and are basically in agreement with the predictions of the Weiss 2_γ state theory except in a region very close to Fe_0.75Pt_0.25. The effect of heat treatments below the ordering temperature is placed in an overall context of competing phase transformations, which can also be used to rationalise conflicting views on the existence of Fe₃Ni, and the role of ordering on the Invar effect in general.     

The magnetic behaviour of diluted CrAl alloys

Magnetic susceptibility as a function of temperature of binary CrAl alloys containing 0.7,1.07,1.35,1.59, 1.79,1.98, 2.18, 2.84, 3.74 and 4.36 at %A1 is investigated. Aluminium, by alloying, acts on the Néel temperature of pure chromium giving rise to a complicated phase diagram. The bahaviour of the magnetic susceptibility as a function of temperature, in the ordered phase, for the samples containing 1.28, 2.18 and 2.84 at %A1 is found to be temperature independent. In the paramagnetic region, for the samples containing between 1.07 and 2.84 at %A1, it is found a decrease of the magnetic susceptibility as a function of temperature.     

Effects of alloying on the band structure of gold: Piezoreflectance measurements on some AuCo and AuV alloys

Piezoreflectance measurements have been made on a series of gold cobalt and gold vanadium alloys with impurity concentrations of up to 4% using a strain amplitude of 4 × 10^?4 at a frequency of 68 kHz. The spectra show that the main interband transitions occur at 2.4, 3.5 and 4.5 eV. The deformation potentials with impurity concentration have been found for these transitions. An additional interband transition was found to occur at an energy of 1.8eV and this was enhanced significantly with impurity concentration. This may be due to the impurity causing a broadening of the d bands and hence a smearing of the interband threshold or alternatively it may be caused by a d band to Fermi level transition along the Δ direction close to the X point.     

Ta 5d band symmetry of 1T-TaS1.2Se0.8 in the commensurate charge-density-wave phase

We present a detailed angle-resolved photoemission study on the layered transition-metal dichalcogenide 1T-TaS1.2Se0.8 in the commensurate charge-density-wave (CDW) phase. A drastic reduction in the spectral weight along the high symmetry line GammaM, particularly around the point M, is observed when s-polarized light was used. This implies that the initial state must be symmetric with respect to a mirror plane perpendicular to the line GammaK, which is consistent with conventional band calculations in the absence of the CDW. We conclude that there is only a limited amount of modification of the electronic structure of 1T-TaS1.2Se0.8 in the commensurate CDW phase due to the CDW-related potential.     

Deconvolution of the XPS-valence band spectrum of gold

Convolution and deconvolution are discussed when applied to XPS-profiles. A comparison of theoretical and experimental distributions (gold valence band) shows some very interesting features.     

Bandgaps and band bowing in semiconductor alloys

The bandgap and band bowing parameter of semiconductor alloys are calculated with a fast and realistic approach. The method is a dielectric scaling approximation that is based on a scissor approximation. It adds an energy shift to the bandgap provided by the local density approximation (LDA) of the density functional theory (DFT). The energy shift consists of a material-independent constant weighted by the inverse of the high-frequency dielectric constant. The salient feature of the approach is the fast calculation of the dielectric constant of alloys via the Green function (GF) of the TB-LMTOs (tight-binding linear muffin-tin orbitals) in the atomic sphere approximation (ASA). When it is applied to highly mismatched semiconductor alloys (HMAs) like Zn Te_xSe_1?x, this method provides a band bowing parameter that is different from the band bowing parameter calculated with the LDA due to the bowing exhibited also by the high-frequency dielectric constant.     

The elastic behaviour of In-Tl alloys in the vicinity of the martensitic transition

To test further the prediction of collapse of the [110], q|| [11̄0] acoustic mode at the martensitic phase transition, pulse superposition measurements of ultrasonic wave velocities have been made in indium-thallium alloys containing 25 and 27 at. % thallium. These alloys are f.c.c. at room temperature and transform on cooling to the f.c.t. phase at 196 ± 2°K and 127 ± 2°K, respectively. Results show that $\text{1}\text{2}$(C₁₁ ? C₁₂) goes to zero within experimental error at the transition temperature. The room temperature elastic constants of the tetragonal 11.5 and 15 at. % thallium alloys are also reported.     

Investigation of valence band structures in Cu-Pd alloys

With the use of a HP 5950 A spectrometer X-ray photoelectron spectra (XPS) of valence band were obtained for Cu-Pd alloys and the density of electron states was calculated by the coherent potential method. It is found that d-resonance states of Pd are present in the alloys containing a high percentage of copper but there are no apparant d-resonance states of Cu in the alloys containing a high percentage of palladium.     

Dynamics of slip band formation in fcc alloys

The problems induced by the inhomogeneity of deformation of alloys with high solute concentration are discussed using experimental results on Cu-2...10% Ni and Cu-30% Zn single crystals. Combining microscopic observations (etch-pit/stress-pulse method) with mesoscopic studies (microcinematography of slip line formation) and with macroscopic measurements (stress relaxation) in terms of the effective activation volumes, it is inferred that theories on the motion of a dislocation across the obstacle field in the slip plane can be compared with microscopic (etch-pit) results, while the macroscopic deformation kinetics and the critical resolved shear stress in the yield region of inhomogeneously deformed alloys might rather be controlled by the transfer process of slip to neighbouring slip planes.Fruitful discussions with Prof. Ch. Schwink and Dipl.-Phys. A. Hampel, as well as the continuous financial supports by the Deutsche Forschungsgemeinschaft, now in project A9 of SFB 319 are gratefully acknowledged.     

Optical investigation of the band structure of Ge-Si alloys

The reflection spectra of Ge-Si alloys have been measured at room temperature in the photon energy range 2–5 eV. The curve giving the dependence of the energy of the first characteristic peak in the reflection spectrum on the composition of the alloy shows a break at about 79 at. per cent of Si. The consequences of this observation for the band structure are discussed.     

Superparamagnetic-like behaviour of magnetic alloys

The effect of antiferromagnetic interaction on a binary Ising ferromagnetic alloy A_pB_1?p is studied based on cluster-variational method and assuming either J_AB or J_BB or both exchange interactions to be of antiferromagnetic type. In a ferromagnetic state the moment saturates to a value much lower than its full value. Within the temperature interval where moment saturates, the system exhibits superparamagnetic-like behaviour. The induced moment becomes a function of $\text{h}\text{T}$ only, and the zero-field susceptibility follows Curie law. The incomplete saturation of moment persists up to a large value of $\text{h}\text{T}$. The short-range order parameter at T = 0 is much less than that of homogeneous ferromagnet.     

Kondo behaviour in hydrogenated Pd-Co alloys

Pd-Co-H_x alloys with x in the 0.75 range present resistivity minima as a function of temperature typical of Kondo behaviour. It is found that the concentration x is a critical factor for these observations and several explanations are proposed.     

Magnetoreflection studies on the band structure of antimony-bismuth alloys

A magnetoreflection study of Sb rich SbBi alloys is presented which indicates departures from the Tichovolsky-Mavroides interpolation scheme for the T-point band gap. Line shape peculiarities due to n_v ≠ n_c transitions, similar to those found in As and Sb, have been observed which suggest relocation of the band extrema in the Brillouin zone.     

Magnetoelastic behaviour in amorphous FePGa alloys

Temperature dependences of Young's modulus and saturation magnetization, linear and forced volume magnetostriction were measured for FePGa amorphous alloys. A discussion concerning the influence of linear magnetostriction, forced volume magnetostriction and magnetic ordering on the changes of E(T) function was made. It was found that annealing of the sample decreases the linear magnetostriction contribution increasing the other two contributions at the same time.     

Heterojunction band discontinuities of quaternary semiconductor alloys

A simple sp³ hybrid-orbital model for predicting valence-band discontinuities is proposed and applied to quaternaries. The effects of anion and cation disorder are taken into account explicitly within the coherent-potential approximation. Results for In_1?xGa_xP_1?yAs_y, In_1?xGa_xAs_1?ySb_y, Ga_1?xAl_xAs_1?ySb_y and In_1?xAl_xP_1?ySb_y lattice-matched to some binaries are shown. The broadening of valence-band-top levels due to alloy scattering is found negligible.