Specific heat of Eu x Sr1−x Te

In this paper, we report on measurements of the specific heatC of single-crystalline Eu _x Sr_1–x Te at temperatures between 60 mK and 15 K and in magnetic fields up to 6 T. Pure antiferromagnetic EuTe shows unusual critical behavior in the vicinity of the Néel temperatureT _N=9.8 K with a positive critical exponent instead of the 3d-Heisenberg exponent =–0.12. Possible reasons for this discrepancy between theory and experiment include magnetic anisotropy effects due to magnetic dipole-dipole interactions, which may give rise to a cross-over of the critical behavior very close toT _N. This anisotropy is also seen in the specific heat below 1 K where an exponential decay ofC is observed, and in the dependence of the magnetic susceptibility on the direction of the applied field. With increasing dilution of EuTe with nonmagnetic Sr, the critical behavior changes: becomes negative and decreases continuously towards –1 atxx _c. This concentration dependence of was previously observed in the diluted ferromagnetic system Eu _x Sr_1–x S. Our data thus support that the apparent change in the critical behavior depends on the degree of disorder. Samples with concentrationx lower than the critical concentrationx _c reveal spin-glass behavior in the specific heat. In addition, the dependence ofT _N on magnetic fields is discussed. The data yield a normalized magnetic phase boundaryB _c(T)/B_c(T=0) vs.T _N(B)/T_N(B=0) which is independent of concentration.     

Anomalies of the static dielectric constant of Pb1−x Ge x Te

The static dielectric constant of Pb_1–x Ge _x Te (0x0.05) has been determined from differential capacitance measurements on Schottky-barriers in the temperature range of 4.2–300 K. A comparison with data deduced from the phonon frequencies via the Lyddane-Sachs-Teller relation shows substantial discrepancies which are attributed to lattice defects.Work supported by Jubiläumsfonds der Österreichischen Nationalbank     

Thermal conductivity of single crystals of the Ca1 − x Y x F2 + x solid solution

The thermal conductivity of single crystals of the solid solution of yttrium fluoride in calcium fluoride Ca_{1 ? x} Y _x F_{2 + x} with the fluorite structure (x ≤ 0.20) and the Ca_0.27Y_0.73F_2.73 phase with the tisonite structure has been studied by the absolute steady-state longitudinal heat flow method in the temperature range 50–300 K. It has been established that the thermal conductivity drops sharply with increasing yttrium trifluoride concentration, especially in the low-temperature region.     

The crystallization of Fe1−x P x , 0.09≦x≦0.26

The crystallization behaviour of about 60 samples of electrodeposited Fe_1–x P _x , 0.09<x<0.26, was investigated with DSC and X-ray diffraction. Several subsequenting transformations during heating at 10 K/min were identified. The corresponding transformation temperatures, reaction heats and reaction rates were measured. If the as-deposited samples contain metal-rich crystallites (microcrystalline and partly amorphous material) crystallization starts with primary precipitation of -iron followed by polymorphous crystallization of Fe₃P. In amorphous samples these two processes become less important compared with the eutectoid reaction the higher the phosphorus content. In a small concentration range around 19 at% P this transformation is the only one. Above this range the primary crystallization of Fe₃P becomes more and more dominant.     

Study of electrical and thermoelecrical properties of sulfides Tm x Mn1–x S

Variable-valence Tm _x Mn_1–x S (0 ? x ? 0.15) compounds have been synthesized and their structural, electrical, and thermoelectrical properties have been studied in the temperature range of 80–1100 K. The regions of existence of solid solutions of sulfides Tm _x Mn_1–x S with the NaCl-type fcc lattice have been determined. It has been found that, as thulium ions are substituted for manganese cations, the electrical resistivity increases, and the lattice parameter increases more sharply than that corresponding to the Vegard’s law. The study of the temperature dependences of the thermopower coefficient has revealed that the current carrier sign is retained to 500 K for all the substitution concentrations, and the charge carrier type changes from the hole type to the electron type with variations in the temperature. The experimental data have been explained in terms of the exciton model.     

Magnetic properties of amorphous Mn x B100−x alloys

Magnetic properties of amorphous Mn _x B_100–x alloys ranging fromx = 30 to 70 under high magnetic fields and low ac magnetic fields in the temperature range from 4.2 K to room temperature have been investigated. Samples which have Mn concentrations of aboutx = 40–60 show spin-glass-like properties in the low-temperature region. This spin-glass characteristics result from a frustration in the spin system which is caused by the competition of ferromagnetic and antiferromagnetic interactions between randomly distributed Mn atoms. Both magnetization at 4.2 K and paramagnetic momentP _eff as a function of Mn concentration show a peak aroundx 44 which drops rapidly towards both sides of the Mn content.     

Lattice dynamics of ZnSe x S1 − x semiconductor crystals

Recently ultrabroadband infrared solid state lasers based on a new vibronic material Cr²⁺:ZnSe _x S_1–x were demonstrated [1–3]. Cr²⁺ ion substitutes the metal ion (tetrahedral sites), the crystal field of the solid solution is responsible for large inhomogeneous broadening of Cr²⁺ electron states. The crystal field can be reconstructed by investigation of lattice dynamics — optical phonon parameters and dielectric function in IR. We paid special attention to investigation of vibrational and infrared spectroscopic properties of ZnSe _x S_{1 ? x} crystals. A very interesting and somewhat unexpected result of these studies was the existence in the crystals of effective S-Se dipoles, which generate an additional deep dynamically charged level in the forbidden gap of the semiconductors. The results of the first-principles calculations of both the phonon structure and the electron localization in ZnSe _x S_1–x crystals as well as acceptor levels in Cr²⁺: ZnSe crystal are discussed.     

Features of the plasma sputtering of polycrystalline Pb1 − x Sn x S films

The processes of the sputtering and modification of surfaces of polycrystalline films of the ternary solid solution Pb_{1 ? x} Sn _x S (x = 0.9–1.0) in a high-density Ar plasma of high-frequency low-pressure inductive discharge are studied. Films with thicknesses of 1–4 μm are grown on glass substrates using the “hot-wall” method and consist of plate-like crystallites. It is established that the sputtering rate for lead-tin sulfide films does not exceed 2.0 nm/s, which is determined by the presence of oxygen-containing compounds on the surfaces. In the case of plate-like crystallites with nanodimensional thicknesses, the effect of smoothing of the developed surfaces of the polycrystalline Pb_{1 ? x} Sn _x S layers during plasma treatment is observed; this is important for fabricating multilayer device structures.     

Effect of pressure on electrical properties of SnS x Se1−x single crystals

The single crystals of tin monosulphoselenides in the form of a series SnS _x Se_1?x (where x?=?0, 0.25, 0.50,0.75 and 1) have been grown using the direct vapor transport technique (DVT). The analysis of the X-ray diffraction patterns reveals that all crystals belong to the orthorhombic crystal structure. Hall effect measurements were carried out on grown crystals at room temperature. The optical absorption measurements at room temperature have been carried out for all crystals. The values of the band gap were determined at atmospheric pressure and also calculated at high-pressure. Simultaneous thermoelectric power (TEP) and a.c. resistance measurements up to 8?GPa were carried out. The results of the effect of high-pressure on the electrical resistance of the grown crystals are reported in this paper.     

Structural deformations of the cubic lattice of the Zn1 ? x Fe x Se (x = 0.001) crystal

The structural state of a Zn_{1 ? x} Fe _x Se (x = 0.001) crystal has been studied using thermal neutron diffraction. The diffraction patterns of the cubic crystal have been found to contain diffuse scattering regions concentrated in the vicinity of the strong Bragg reflections. It has been shown that the diffuse scattering effects are due to local transverse displacements of the crystal lattice atoms, and these displacements are induced by iron ions that demonstrate the static Jahn-Teller effect of the tetragonal type in the ZnSe compound.     

Density of states of substoichiometric TiN1−x

The electronic states of substoichiometric TiN_1–x are studied by the CPA method and both the partial and total densities of states (DOS) are calculated. The results reveal that with increasing vacancy concentrationx the Fermi levelE _F moves to higher energies and the DOS atE _F,g(E _F), increases linearly. The calculated L_{II, III} X-ray spectra of Ti compare well with experiment.Work supported by the Research Institute for Powder Metallurgy, Sumperk, Czechoslovakia.The author is indebted to Dr. B. Velický, CSc for suggestion of the method to solve the Soven's equation. The financial assistance of the Research Institute for Powder Metallurgy, umperk, Czechoslovakia is gratefully acknowledged.     

Formation of Ti1–x Si x and Ti1–x Si x N films by magnetron co-sputtering

The paper reports on surface morphology, structure and microhardness of TiSi–N films formed by cosputtering from two target-facing unbalanced magnetrons, equipped with pure Ti and Si targets, on an unheated substrate rotating in front of both targets. The ratio Si/Ti in the TiSi–N film was achieved by modifying the magnitude of currents in the individual magnetrons and by the addition of nitrogen to the film. The rotation of the substrate has a strong effect on the film deposition rate and its morphology. The deposition rate is 3 times lower than that of the film deposited on a stationary substrate. The surface roughness of a polycrystalline Ti film deposited on the rotating substrate is considerably higher than that on a stationary substrate. On the contrary, the surface of an amorphous Si film is smooth and there is no difference between the roughness of Si films sputtered on stationary and on rotating substrates. The hardness of the film increases with increasing Si content and with the addition of nitrogen to the TiSi film. The Ti(26 at.%)Si(8.5 at.%)N(65 at.%)-film sputtered on an unheated rotating steel substrate, held at a floating potential, exhibited the best result with a hardness of 29 GPa.     

Influence of grain boundaries on resistivity of manganites La1 − x K x MnO3

Results of investigation of resistivity and magnetoresistance of manganites La_{1 − x} K _x MnO₃ (x = 0.050–0.175) are presented. Behavior of resistivity ρ(T) in the paramagnetic and ferromagnetic phases has been described. To describe ρ(T) near the phase-transition temperature, notions of the percolation theory have been used. Two maxima have been found in the dependence ρ(T); their appearance has been attributed to the ceramic nature of the studied samples. The observed increase in magnetoresistance with a decrease in temperature is caused by intergranular spin-polarized tunneling of charge carriers.     

Compositional dependence of the optical properties of amorphous Se100– x Te x thin films

Thin films of amorphous Se_{100 –x} Te _x with different compositions (x = 10, 20, 30 and 40 at%) were deposited on glass substrates by thermal evaporation. Transmission spectra T(λ) of the films at normal incidence were obtained in the spectral region from 400 to 2500 nm. A straightforward analysis proposed by Swanepoel [J. Phys. E: Sci. Instrum. 17 896 (1984)], using of the maxima and minima of the interference fringes, was applied to derive the real and imaginary parts of the complex index of refraction plus film thickness. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple and DiDomenico model [Phys. Rev. B 3 1338 (1971)]. The optical band gap was determined from the spectral dependence of the absorption coefficient using the Tauc formula [in The Optical Properties of Solids, edited by F. Abeles (North Holland, Amsterdam, 1970), p. 227]. The refractive index increases and the optical band gap decreases with increasing tellurium content.     

Laser radiation of Cd x Zn1−x S semiconductor targets of the gas diode

The experimental results on the study of radiation of Cd _x Zn_1?x S semiconductor targets (STs) of the gas diode (GD) for the pressure variation from 10^?1 Torr to the atmospheric pressure are presented. Pulses 0.5–1 ns long with an amplitude to 200 kV were applied to the GD cathode. Laser radiation (509 nm) was generated in the ST under a beam of accelerated runaway electrons to a pressure of 2.5 Torr. At atmospheric pressure, generation in the ST was observed in discharge channels when the streamer moved from one ST surface to another. In this case, as the electric fields strength increased, radiation sequentially arose at three spectral lines, 509, 480, and 469 nm. Possible causes of the observed phenomena are considered.     

Mössbauer spectroscopic study of FeAl1−x Co x

We report the results of a Mössbauer study of the alloy sytem FeAl_1?x Co _x forx ≥ 0.3 at temperatures down to 83 K. Magnetic splitting is observed forx ≥ 0.35 at all temperatures. However, forx=0.3, no splitting is observed at room temperature, and superparamagnetic behavior occurs at LN₂ temperature. The magnetically split spectra are fitted each with a distribution of hyperfine fields and the average hyperfine field \(\bar B_{hf} \) as a function of temperature is obtained. The variation of \(\bar B_{hf} \) withT is explained using the model of magnetic clusters with collective magnetic excitations from which the saturation hyperfine field and the magnetic anisotropy energy for these clusters are obtained. Also, the results are discussed using the model of random atomic distributions, and the agreement between the calculated and the experimentally obtained distributions of hyperfine fields is found improve asx increases.     

The influence of praseodymium concentration on the luminescence properties of Ca1 ? x Pr x F2 + x (0.002 ≤ x ≤0.35)

The possibility of implementing photon cascade emission in CaF₂-PrF₃ crystals by increasing the PrF₃ concentration in the CaF₂ matrix is studied. It is shown that an increase in the Pr³⁺ content leads to redistribution of radiative transitions in favor of the ¹ S ₀-luminescence. The decrease in the efficiency of the second step of photon cascade emission at high PrF₃ concentrations is caused by quenching of the ³ P ₀ ?? 4f ² transitions as a result of cross relaxation.     

Heat capacity of multiferroics Bi1–x Pr x FeO3

Physics of the Solid State - The heat capacity of multiferroics Bi1–x Pr x FeO3 (0 ≤ x ≤ 0.20) has been studied in the temperature range 130–800 K. An insignificant...     

The superconducting transition temperature of Pb1−x Mn x films

Results of the superconducting transition temperatureT _c of amorphous and microcrystalline films of lead doped with manganese as magnetic impurity are reported in this work. The amorphous films show an Abrikosov-Gor'kov behaviour, whereas for the crystalline films there is a much smaller depression and a peak for higher Mn concentrations, which indicates a region of coexistence of superconductivity and magnetic ordering as a spinglass.Supported by the Deutsche Forschungsgemeinschaft in the Sonderforschungsbereich 125, Fehlordnung in Metallen — Aachen, Jülich, Köln     

Structural and electronic properties of GaN x As1−x alloys

The structural and electronic properties of cubic GaN _x As_1−x with N-concentration varying between 0.0 and 1.0 with step of 0.25 were investigated using the full potential–linearized augmented plane wave (FP-LAPW) method. We have used the local density approximation (LDA) and the generalized gradient approximation (GGA) for the exchange and correlation potential. In addition the Engel-Vosko generalized gradient approximation (EVGGA) was used for the band-structure calculations. The structural properties of the binary and ternary alloys were investigated. The electronic band structure, total and partial density of states as well as the electron charge density were determined for both the binary and their related ternary alloys. The energy gap of the alloys decreases when we move from x=0.0 to 0.25; then it increases by a factor of about 1.8 when we move from 0.25 to 0.5, 0.75 and 1.0 using EVGGA. For both LDA and GGA moving from x=0.0 to 0.25 causes the band gap to close, showing the metallic nature of the GaN_0.25As_0.75 alloy. When the composition of N moves through x=0.25, 0.5, 0.75 and 1, the band gap increases.