Search

The phase and elemental composition and the temperature dependences of the resistivity and Hall coefficient (temperature range 4.2 K ≤ T ≤ 300 K, magnetic fields B ≤ 0.07 T) are studied in Pb1 – x– ySnxFeyTe alloys with varying matrix composition and iron-impurity concentration along single-crystal ingots synthesized by the Bridgman–Stockbarger method. The distributions of tin and iron along ingots are obtained. Anomalous temperature dependences of the Hall coefficient related to the Fermi-level pinning by the resonance level of iron located in the valence band of the alloys are found. The experimental results are analyzed within the model of transformation of the electronic structure, involving iron level movement with respect to the top of the valence band with increasing tin concentration and temperature. The temperature coefficient of the iron level movement with respect to the midgap is determined. Possible diagrams of transformation of the electronic structure with increasing temperature in alloys with the normal spectrum (0.06 ≤ x ≤ 0.35) are proposed. [ABSTRACT FROM AUTHOR]

The field and temperature dependences of the magnetization (magnetic fields B ≤ 7.5 T, temperatures T = 2.0-75 K) of samples from a Pb1-x-ySnxVyTe (x = 0.08, y = 0.01) single-crystal ingot synthesized by the Bridgman-Stockbarger method. It is established that the sample magnetization contains two main contributions, notably, the paramagnetism of vanadium ions and diamagnetism of the crystal lattice. The field and temperature dependences of the magnetization are approximated by the sum of modified Brillouin functions corresponding to the paramagnetic contributions of vanadium in two different charge states and the diamagnetic contribution linear in terms of field. The concentrations of vanadium ions in two different magnetic states and the character of their variation along the ingot are determined within the scope of the alloy’s electronic-structure rearrangement because of doping. The results are compared with the data of X-ray fluorescence microanalysis and the results of studying the galvanomagnetic properties of the samples. [ABSTRACT FROM AUTHOR]

The field dependences of the magnetization (temperatures T = 2.0-70 K, magnetic fields B ≤ 7.5 T) of the samples from a single-crystalline Pb1 - yFeyTe ingot (y = 0.02) grown by the Bridgman method are studied. It is established that the sample magnetization contains several major contributions such as the paramagnetism of iron ions, diamagnetism of the crystal lattice, and the contributions of charge carriers and clusters of iron atoms. The field dependences of the paramagnetic contribution of iron ions and the contribution of clusters of iron atoms are approximated by theoretical dependences based on the Brillouin and Langevin functions, respectively. The average concentrations and magnetic moment of clusters as well as the total magnetic momentum of clusters in the volume unit in the samples upon increasing the impurity concentration along the ingot are determined. [ABSTRACT FROM AUTHOR]

The temperature dependences of the Hall coefficient (4.2 K ≤ T ≤ 300 K, B ≤ 0.07 T) in PbGeCrTe alloys ( x = 0.03-0.08, y ≤ 0.01) are studied. An increase in the absolute value of the Hall coefficient with an increase in temperature is found. This fact is indicative of a decrease in the concentration of free electrons as a result of the motion of the resonant level of chromium stabilizing the Fermi level relative to the conduction-band bottom. The temperature dependences of the Hall coefficient, in satisfactory agreement with the experimental ones, are calculated in the context of the two-band Kane dispersion law allowing for the structural phase transition upon increasing temperature. The energy position and temperature coefficients of the motion of the resonant level of chromium relative to the middle of the band gap in the rhombohedral and cubic phases are determined. [ABSTRACT FROM AUTHOR]

Magnetic properties of Pb1 − x − yGe xCr y Te alloys ( x = 0.02–0.20, y = 0.01–0.08) were studied. It was detected that the magnetic susceptibility of alloys consists of two contributions: the paramagnetic Curie-Weiss part (the temperature region is T < 50 K) caused, probably, by the Cr3+ ion paramagnetism, and the high-temperature ferromagnetic part ( T < 300 K). The dependences of the concentration of magnetic centers on the composition of the matrix were obtained from the paramagnetic and ferromagnetic contributions. It was shown that a decrease in the concentration of paramagnetic centers can be, at least qualitatively, explained by the transformation of the electronic structure as the germanium concentration increases. A phenomenological model was suggested, which explains the behavior of magnetic properties as the chromium content increases, and possible mechanisms of ferromagnetic ordering in studied alloys are discussed. [ABSTRACT FROM AUTHOR]

The electrical properties of chromium-doped n-Pb1− x Ge x Te alloys ( x = 0.02–0.13) have been studied. A decrease in the free-electron concentration and a metal-insulator transition are observed as the germanium content of alloys increases. This is due to the Fermi level pinning by the chromium impurity level and to the flow of electrons from the conduction band to the impurity level. The experimental data obtained are used to calculate, in terms of the two-band Kane dispersion law, the dependences of the electron concentration and Fermi energy on the germanium content in the alloy. The motion rate of the chromium-related level with respect to the conduction band bottom is determined and a model of variation of the electronic structure with the matrix composition is suggested. [ABSTRACT FROM AUTHOR]

The effect of pressure on electrical properties of the n-Pb1− x SnxTe alloy ( x = 0.21) doped with gallium is studied. A decrease in the free-electron concentration with increasing temperature and an increase in this concentration with increasing pressure are observed; these observations indicate that the Fermi level is pinned at the resonant gallium level. The two-band Kane’s dispersion law and experimental data were used to calculate the pressure dependences of the electron concentration and Fermi level. A diagram of transformation of the charge-carrier energy spectrum in Pb1− x SnxTe:Ga subjected to pressure is suggested; the rate of the shift of the gallium resonant level in reference to the midgap under the effect of pressure is determined. [ABSTRACT FROM AUTHOR]

Electrical properties of gallium-doped n-Pb1− x SnxTe alloys ( x=0.09−0.21) are studied. Ahomalous temperature dependences of the Hall coefficient which indicate the Fermi level pinning by a resonant gallium level in the conduction band were detected. The dependences of the electron concentration and Fermi energy on the alloy composition and temperature are calculated from experimental data in terms of the two-band Kane dispersion relation. It is shown that the gallium resonant level position relative to the valence band top is almost independent of the matrix composition. The dependence of the thermal coefficient of the resonant level shift with respect to the midgap on the alloy composition is obtained. [ABSTRACT FROM AUTHOR]

The effect of pressure on electrical properties of Ga-doped n-Pb1 – xGexTe alloys (x = 0.06, 0.08) is studied. The pressure dependence of the activation energy of a deep Ga impurity center is obtained. It is shown that the position of the Ga level with respect to the bottom of the conduction band is virtually unchanged under pressure. Anomalies are found in the temperature and pressure dependences of the resistivity; these anomalies are apparently associated with structural phase transitions from the cubic to the rhombohedral and orthorhombic phases, respectively. The results obtained are used to construct a diagram of the modification of the energy spectrum of charge carriers in the cubic phase of the alloys investigated under pressure. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

The kinetics of the variation of the electron concentration in electron-irradiated (T≈300 K, E=6 MeV, Φ≤7.1 × 10[sup 17] cm[sup -2]) n-Pb[sub 1 - x]Sn[sub x]Se (x = 0.2 and 0.25) alloys in the vicinity of the metal-insulator transition induced by electron irradiation are investigated. The principal parameters of the energy spectrum of the irradiated alloys are determined by comparing the experimental and theoretical dependences of the electron concentration on fluence. It is shown that agreement between the theoretical and experimental data is possible only under the assumption that the defect production rate decreases with increasing fluence, and a model, within which the main defect formation mechanism in the alloys investigated is the formation of complexes of primary radiation defects with structural defects typical of the as-grown crystals, is proposed. [ABSTRACT FROM AUTHOR]

The effect of electron bombardment (T[sub irr] ... 300 K, E=6 MeV, Φ ≤ 4 × 10[sub 17] cm[sup -2]) on the electrical properties of n-type Pb[sub 1 - x]Sn[sub x]Te has been studied. Electron bombardment decreases the electron concentration and produces conductivity-type n-p conversion. The difference rate of the donor- and acceptor-type defect generation as a result of bombardment has been determined. Anomalies are detected in the temperature and magnetic-field dependences of the electrical parameters of the bombardment samples. These anomalies are associated with the appearance of a hole-enriched surface layer as a result of electron bombardment. [ABSTRACT FROM AUTHOR]

Temperature dependences of magnetic susceptibility and magnetic-field dependences of magnetization in the Pb[sub 1-x] Ge[sub x]Y[sub b]Te (0 ≤ x ≤ 0.02, y ≤ 0.065) solid solutions were studied It was found that diamagnetic response was replaced by the Curie-Weiss paramagnetic response as temperature decreased. This indicates that Yb[sup 3+] (4f[sup 13]) magnetic ions are present in the alloys. The magnetic ion concentration and the occupancy of the Yb-induced impurity band were determined from the experimental data. [ABSTRACT FROM AUTHOR]

Galvanomagnetic properties of gallium-doped Pb[sub 1 - x]Ge[sub x]Te (0.04 ≤ x ≤ 0.08) alloys were studied. It is shown that gallium doping induces a deep impurity level in the alloy band gap; the energy position of this level depends on the germanium content in the alloy. A model assuming that doping with gallium results in the emergence of two defect levels in the energy spectrum of the alloys is proposed. [ABSTRACT FROM AUTHOR]

The effect of hydrostatic pressure (P ≤ 12 kbar) on the electrical properties of n-type Pb[sub 1-x]Sn[sub x]Te (x = 0.22) bombarded by electrons (T ≈ 300 K, E= 6 MeV, Φ = 7.7 × 10[sup 17] cm[sup -2]) has been investigated. The restructuring of the energy spectrum of electronirradiated alloys under pressure has been investigated. The parameters of a model of the energy spectrum of charge carriers in electron-irradiated n-type Pb[sub 1-x]Sn[sub x]Te (x = 0.22) have been determined on the basis of the experimental data obtained. [ABSTRACT FROM AUTHOR]