Superstructures in cubic A II B VI crystals heavily doped with Ni and V ions
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RACTION AND SCATTERING OF NEUTRONS
Superstructures in Cubic AIIBVI Crystals Heavily Doped with Ni and V Ions V. I. Maksimov, S. F. Dubinin†, and T. P. Surkova Institute of Metal Physics, Ural Branch, Russian Academy of Sciences, Yekaterinburg, 620990 Russia e-mail: [email protected] Received March 6, 2015
Abstract—Specific features of the crystal structure of bulk sphalerite-type Zn0.9Ni0.1S, Zn0.9V0.1Se, and Zn0.997Ni0.003Te crystals have been investigated in detail by thermal-neutron diffraction at room temperature. Fine effects (indicative of the existence of distortion microdomains, nucleation of long- and short-wavelength modulations, and tendencies toward local lowering of the symmetry based on the initial cubic structure) can be observed in the obtained scattering patterns. Various states preceding the fcc ↔ hcp phase transition have been revealed in these crystals. They depend on the elemental composition and are formed upon the reaction of the initial lattice to perturbations induced by foreign ions with an incomplete 3d shell. DOI: 10.1134/S1063774516010120
INTRODUCTION АIIВVI
Doping of binary compounds with magnetoactive ions makes it possible to prepare diluted magnetic semiconductors (DMSs) and promising materials for electron optics [1, 2] and spintronics [3]. The main stable structural modifications of the compounds, containing chemical elements of the II–VI groups, are zinc blende, or sphalerite (fcc lattice), and related wurtzite (hcp structure), which have similar local tetrahedral coordinations of atoms [4]. The suggestion about the possibility of replacing cations in semiconductors with magnetic atoms having incomplete d and f electron shells is favored by the results of numerous optical studies [5]. Poor solubility in semiconductor matrices of (II–VI)-group elements is generally typical of 3d ions. An exception is manganese ions with a natural solubility limit of several tens of atomic percent in the bulk of ZnВVI material (ВVI = S, Se, or Te) [4]. With an increase in the Mn concentration, the cubic modification based on ZnS and ZnSe remains only below a certain doping level, an excess of which leads to stabilization of the hexagonal phase. To date, there are no detailed diagrams of solubility of other 3d ions in wide-gap semiconductors of the II–VI groups. Doping with 3d atoms, characterized by nonsphericity of d electron shells, strongly destabilizes the initial crystal structure of the semiconductors containing (II–VI)-group elements, producing local distortions and strains in the lattice [5, 6]. A tendency of the initial compounds toward polymorphism and polytypism † Deceased.
additionally complicates the physical pattern of change in the properties as a result of the doping [5, 7]. It was shown earlier using neutron scattering that 3d atoms (V, Cr, Fe, and Ni), which are incorporated into the matrix of (II–VI)-group elements even in small amounts (~0.001 per formula unit), lead to the formation of inhomogeneous nanoregions in the crystal structure. Self-organization effects can occur i
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