V. D. Parkhomenko

Inhomogeneous lattice distortions in a Zn1 − xCrxSe crystal

The structure of a Zn1−xCrxSe semiconductor crystal with x = 0.0029 was studied using thermal neutron diffraction. It was detected that the diffraction patterns of the crystal contain regions of diffuse scattering concentrated in the vicinity of the strong Bragg reflections. It was shown that the diffuse scattering was caused by transverse displacements of lattice atoms induced by chromium impurities, which undergo static tetragonal Jahn-Teller distortions in ZnSe.

Nanoscale distortions of the lattice of a ZnSe crystal doped with 3d elements

The structure of semiconductor crystals Zn1−xVx2+Se (x = 0.0018) and Zn1−xCrx2+Se (x = 0.0006) was studied for the first time using thermal neutron diffraction at 300 and 120 K. The diffraction patterns of the crystals were revealed to contain diffuse scattering regions near the Bragg reflections of the initial cubic lattice. The experimental results are discussed in combination with earlier obtained data on neutron diffraction and propagation of ultrasonic waves in Zn1−xNix2+Se (x = 0.0025) and Zn1−xCrx2+Se (x = 0.0029). The diffuse scattering is shown to be due to nanoscale shear strains of the ZnSe lattice. The character of these strains is determined by Jahn-Teller 3d ions.

Magnetic state of a Zn1 −xCrxSe bulk crystal

The spin system of a Zn1 −xCrxSe bulk crystal (x = 0.045) was studied using thermal-neutron diffraction and magnetic measurements. Previously, it was reported in the literature that thin films (∼200 nm thick) of this type of semiconductors exhibit a ferromagnetic order. In this study, the ferromagnetic order is found to be absent in the bulk crystal.

Lattice Instability Induced by 3d Impurities in II–VI Compound Semiconductors

Nickel-impurity-induced transverse displacements of ions in a Zn1−xNixSe lattice (x = 0.0025) were detected. This type of displacement correlates with macroscopic distortions of a crystal associated with transverse ultrasonic waves that are propagated along the 〈110〉 direction. The shear instability is assumed to be due to the hybridization of the sp3 bonds with the 3d states of the impurity centers.

Effect of doping with nickel ions on the structural state of a zinc oxide crystal

The fine structure of a hexagonal zinc oxide crystal doped with nickel ions of the composition Zn1 − xNixO has been studied using neutron diffraction and magnetic measurements. It is established that even at very low doping levels (x = 0.0004), the crystal undergoes local distortions in basal planes of the initial hexagonal lattice. The local distortions are assumed to be sources of the formation of ferromagnetism in compounds of this class.

Fine structure and magnetism of the cubic oxide compound Ni0.3Zn0.7O

The fine structure and spin system of the cubic oxide Ni0.3Zn0.7O compound prepared from the initial hexagonal phase by quenching a sample with a high temperature and applying an external hydrostatic pressure to it have been studied using magnetic measurements, synchrotron and X-ray diffraction. It has been revealed that the diffraction patterns of this compound contain a system of weak diffuse maxima with the wave vectors q = (1/6 1/6 1/6)2π/a and (1/3 1/3 1/3)2π/a, along with strong Bragg peaks of the cubic phase. It has been shown that the origin of the diffuse peaks is due to longitudinal and transverse displacements of ions with respect to symmetric crystallographic directions of the {111} type. The reasons for the ion displacement and specific features of the structure of the spin system of the strongly correlated oxide Ni0.3Zn0.7O compound have been briefly discussed.

Structural and magnetic state of a lightly doped Zn1 − xVxTe crystal

The specific features of the structure and the spin system of a lightly doped Zn1 − xVxTe (x = 0.0002) crystal have been investigated for the first time using thermal neutron diffraction and magnetic measurements. The results of these experiments have been discussed in a close connection with the previously obtained information on neutron diffraction and magnetism in Zn1 − xVxSe (x = 0.0018) and Zn1 − xCrxSe (x = 0.0029, x = 0.0450) single crystals.

Dynamic Deformations of the Crystal Lattice of Sphalerite in the Zn1−x Co x Se(x=0.01) Compound

Local distortions of the crystal lattice of the semiconductor compound Zn1 − xCoxSe (x = 0.01) have been investigated using thermal neutron diffraction. It has been found that the diffraction patterns of the crystal contain regions of diffuse scattering in the vicinity of strong Bragg peaks at 300 K. As the temperature decreases, the intensity of diffuse scattering effects substantially decreases. Arguments in favor of the assumption that the origin of the diffuse scattering is caused by the Jahn-Teller vibronic effect are presented.

Charge ordering in crystals of Pr1−x Sr x MnO3 (x = 0.22, 0.24) ferromagnetic manganites

The structural and magnetic states of Pr1−xSrxMnO3 (x = 0.22, 0.24) manganite crystals were studied over a wide temperature range. Measurements of the magnetic susceptibility and electrical resistivity demonstrated that these manganites belong to the class of ferromagnetic semiconductors. Thermal neutron elastic scattering patterns revealed that, in the temperature range 4.2–350 K, the manganites have an orthorhombic structure (space group Pnma) with a well-pronounced cooperative Jahn-Teller effect. Major emphasis was placed on the nuclear magnetic superstructure with a wave vector q = (2π/2a, 0, 2π/2c). It was shown that this superstructure suggests 1/4-type charge ordering in the manganites under investigation.

Ordering of oxygen vacancies in a CaMnO3 − δ perovskite single crystal

The structure of a CaMnO3 − δ perovskite single crystal was studied for the first time using thermal neutron diffraction in the temperature range 300–840 K. It was detected that oxygen vacancies in the crystal are ordered into two types of superstructure. A phase with a relative number of vacancies δ = 1/4 occupies the largest volume fraction of oxide (∼75%); the other volume is occupied by a superstructure with a lower vacancy content (δ = 1/5). The oxygen deficiency in the crystal lattice was determined to be δ = 0.238. The mechanism of oxygen vacancy ordering in the oxide is discussed taking into account its charge state.