AbstractNon‐centrosymmetric orthorhombic single crystals of Cs2Cu1.1(VO)1.9 (P2O7)2 are obtained by spontaneous crystallization from a melt containing CsH2PO4, CuO, and V2O5 in the molar ratio of 2:2:1 (Al2O3 crucible, 850 °C, 72 h).

A non-centrosymmetric orthorhombic diphosphate, Cs2Cu1+x(VO)2−x(P2O7)2 (x=0.1) with a=13.7364(2)Å, b=9.2666(2)Å, c=11.5678(2)Å, Z=4, has been isolated. Its 3D framework is built from Cu atoms in square pyramidal and square planar coordination, VO5 tetragonal pyramids and P2O7 diphosphate groups, sharing vertices. Large channels are fulfilled by cesium atoms. The ESR study reveals a similarity in behaviour of two paramagnetic (Cu and V) subsystems. The temperature dependences of the ESR linewidth and static magnetic susceptibility data present evidences for a cluster type magnetic ordering in the title compound at T⁎=22K. The weakness of the relevant anomalies reflects presumably obvious Cu2+ ions and (VO)2+ units disorder in the system. It is supposed that the charge and geometry of the framework are controlled by the Cu2+/(VO)2+ ratio; its variation may lead to a design of new materials.

The system Cs2−xRbxSnCu3F12 exhibits several different distorted variants of the kagome lattice, which are probed in detail by powder diffraction methods.

A new compound, Rb2Cu3(P2O7)(2), has been obtained from the melt in the Rb-Cu-P-O system. Its monoclinic crystal structure was determined by single-crystal X-ray diffraction: space group P2(1)/c, Z = 2, a = 7.7119(8) angstrom, b = 10.5245(9) angstrom, c = 7.8034(9) angstrom, beta = 103.862(5)degrees at 293 K, R = 0.030. The copper ions show coordination number (CN) 6 (4+2, distorted tetragonal bipyramidal). Trimers of [CuO6] polyhedra sharing cis-edges form together with diphosphate groups of two tetrahedra [P2O7] a microporous 3D framework with channels open along the c direction. The rubidium ions positioned in the channels show CN 10. The new phase is isotypic to Cs2Cu3(P2O7)(2). The regular changes in cell dimensions in the row Cs2Cu3(P2O7)(2) -> Rb2Cu3(P2O7)(2) are caused by the compression of channel volumes due to decrease of the Cu-O-P angles in the framework windows. An electron spin resonance study indicates appearance of short range magnetic correlations below similar to 120 K, long range magnetic order takes place at T-N = 9.2 K as follows from magnetization and specific heat measurements. First principles calculations of the magnetic exchanges indicate that the effective Cu-Cu hopping interactions corresponding to super-super-exchange paths involving P atoms are much stronger than those within the edge-sharing Cu2-Cu1-Cu2 trimer units.

A method for producing quasi-regular ensembles of Co nanocylinders with controllable height in anodic alumina pores on the surface of GaAs structures is improved. Alumina pores are filled by galvanic deposition of cobalt from CoCl 2 solution, which ensures uniform growth of Co in pores. It is established that, even at a small ratio of length of Co nanocylinders to their diameter l/d ≈ 2, the preferred direction of magnetic anisotropy coincides with the axis of nanocylinders.

The crystal structure, composition, galvanomagnetic properties in low magnetic fields (4.2 K ≤ T ≤ 300 K, B ≤ 0.07 T), and the Shubnikov–de Haas effect (T = 4.2 K, B ≤ 7 T) are studied in Pb1−x−ySnxVyTe (x = 0, 0.05–0.18) alloys synthesized by the Bridgman technique with variable vanadium impurity concentrations. It is shown that increasing the vanadium content leads to the formation of regions enriched in vanadium and of microscopic inclusions of compounds with compositions close to V3Te4. In Pb1−yVyTe stabilization of the Fermi level by a deep vanadium level, an insulator–metal transition, and a rise in the free electron concentration are observed as the vanadium content is increased. The variation in the free charge carrier concentration with increasing vanadium concentration in Pb1−yVyTe and Pb1−x−ySnxVyTe (x = 0.05–0.18) alloys is compared. Possible models for rearrangement of the electronic structure in Pb1−x−ySnxVyTe alloys with vanadium doping are discussed.

The galvanomagnetic properties in weak magnetic fields (4.2T300 K, B0.07 T) as well as Shubnikov-de Haas effect (T=4.2 K, B7 T) in the single crystal Pb1-x-ySnxVyTe (x=0.20, y0.01) under hydrostatic compression up to 15 kbar have been investigated. It is shown that under pressure the decrease of activation energy of vanadium deep level, n-p-inversion of the conductivity type at low temperatures and insulator-metal transition take place. In the metallic phase sharp increase of the Hall mobility and appearance of Shubnikov-de Haas oscillations at helium temperature are observed. The pressure coefficient of vanadium level energy is determined and the diagram of the electronic structure rearrangement for Pb1-x-ySnxVyTe under pressure is proposed.

The crystal structure, Sn and V distribution over the length of single-crystal ingots, and galvanomagnetic effects in low magnetic fields (4.2 K ≤ T ≤ 300 K, B ≤ 0.07 T) in Pb 1− x − y Sn x V y Te alloys ( x = 0.05−0.21, y ≤ 0.015) are studied. It is shown that all the samples are single-phase, while the Sn and V concentrations exponentially increase from the beginning to the end of the ingots. Upon doping with V, a decrease in the concentration of free holes and a metal-insulator transition are found. They are related to the appearance of a deep impurity level of V in the band gap, electron redistribution between the level and the valence band, and pinning of the Fermi-level to the impurity level. The shift rate of the V level relative to the conduction band bottom is determined and a diagram of the reconstruction of the electronic structure of the Pb 1 − x − y Sn x V y Te alloy upon varying the host composition is suggested.

We study the galvanomagnetic properties in weak magnetic fields (4.2 ≤ T ≤ 300 K, B ≤ 0.07 T) and the Shubnikov-de Haas effect (T = 4.2 K, B ≤ 7 T) in single crystal Pb1−x−ySnxVyTe alloys under variation of alloy composition (x = 0.05–0.20, y ≤ 0.01) and hydrostatic compression up to 15 kbar. The increase of vanadium impurity content leads to the p-n-conversion and to a transition in the insulating phase due to the pinning of Fermi level by the donor-type deep vanadium impurity level situated under the bottom of the conduction band. We found that pressure induces a decrease of the activation energy of the vanadium level, the n-p-inversion of the conductivity type at low temperatures and an insulator–metal transition. In the metallic phase, a sharp increase of the Hall mobility (up to 3 × 105 cm2 V−1 s−1) and appearance of Shubnikov-de Haas oscillations are observed at helium temperature. The pressure and temperature coefficients of vanadium deep level energy are determined, and the diagram of the electronic structure rearrangement for Pb1−x−ySnxVyTe under pressure is proposed.

We study the structure, composition and galvanomagnetic properties (4.2 <= T <= 300 K, B <= 0.07 T) of the single crystal Pb1-x-ySnxVyTe, Pb1-yTiyTe and Pb1-yScyTe under variation of the alloy composition (x <= 0.20, y <= 0.025). An increase of the impurity content leads to a change in the free carrier concentration due to pinning of the Fermi level by the donor deep impurity levels. The energetic position of these levels in the investigated alloys is estimated.

The structural and magnetic properties as well as the electron paramagnetic resonance in Pb1-xVxTe (х0.7 at.%) solid solutions have been investigated. It was found that the magnetic field and the temperature dependences of magnetization have a paramagnetic character, connected obviously with the paramagnetic contribution of vanadium impurity isolated ions. Electron paramagnetic resonance spectra were measured and the temperature dependence of the g-factor in the temperature range 85-200 K was obtained.

The galvanomagnetic properties (T=4.2–300K, B≤0.08T) of Pb1−x−ySnxVyTe alloys (x=0.06–0.26, y=0.002–0.066) have been investigated. Low temperature activation range of the impurity conductivity on the temperature dependencies of resistivity ρ and of the Hall coefficient RH in the heavily doped samples has been revealed and attributed to the appearance of vanadium-induced deep level in the gap of the alloys. It was found that in insulating phase alloys possess a high photosensitivity to IR excitation at temperatures up to Tc≈40K. In the alloy with x≈0.2 the metal-insulator transition due to the shift of the Fermi level from the valence band to the gap with the increase of the vanadium and tin content and the pinning of the Fermi level by vanadium level were observed. The diagram of electronic structure reconstruction for Pb1−x−ySnxVyTe alloys was proposed.