V. I. Zinenko

Vibrational Spectra and Elastic, Piezoelectric, and Magnetoelectric Properties of HoFe 3 (BO 3 ) 4 and HoAl 3 (BO 3 ) 4 Crystals

Raman spectra of light are obtained for HoFe3(BO3)4 and HoAl3(BO3)4 crystals at various temperatures and are used for determining the frequencies of crystal lattice vibrations at the center of the Brillouin zone. It is also found that the HoFe3(BO3)4 crystal exhibits a phase transition at Tc ≈ 366 K. The magnetoelectric effect in the paramagnetic phase of these compounds is studied experimentally. The lattice vibration frequencies, elastic and piezoelectric moduli, Born dynamic charges, and the high-frequency permittivity are calculated using the density functional method. A peculiar behavior of the transverse acoustic vibration branch is observed in the Γ → Z direction of the Brillouin zone of the HoFe3(BO3)4 crystal. The electric polarization induced by an external field is estimated using the calculated values of piezoelectric moduli and experimental values of magnetostriction.

Lattice dynamics and hydrostatic-pressure-induced phase transitions in ScF3

AbstractNew phase transitions induced by hydrostatic pressure in a cubic (under standard conditions) ScF3 crystal are discovered by the methods of polarization microscopy and Raman scattering. The space groups

Structure, electrical and magnetic properties, and the origin of the room temperature ferromagnetism in Mn-implanted Si

R\bar 3c

Low-temperature strain relaxation in SiGe/Si heterostructures implanted with Ge ions

for Z=2 and Pnma for Z=4 are proposed for the high-pressure phases. A nonempirical computation of the lattice dynamics of the crystal is carried out. It is shown that, under normal pressure, the cubic phase is stable down to T=0 K, while the application of a hydrostatic pressure gives rise to a phonon branch in the vibrational spectrum (between points R and M of the Brillouin zone) with negative values of squares of frequencies. The condensation of soft mode R5 at the boundary point of the Brillouin zone leads to rhombohedral distortion of the cubic structure with the unit cell volume doubling. The calculated frequencies at q=0 of the ScF3 lattice in the distorted rhombohedral phase are real-valued; the number and position of frequencies active in Raman scattering are in accord with the experimental values.

Lattice dynamics of BiFeO3 under hydrostatic pressure

Raman scattering spectra of RbMnCl3 are measured at room temperature under high hydrostatic pressure. The results are interpreted based on first principles lattice dynamics calculations. The experimental data obtained correlate with the calculations in the low frequency domain but disagree slightly in the region of high-frequency vibrations. The transition from the hexagonal to the cubic perovskite phase observed earlier (near 0.7 GPa) was confirmed, and new transitions to lower symmetry distorted phases were discovered (at 1.1 and 5 GPa).

Ferromagnetism of Mn-Implanted Silicon: Magnetization and Magnetooptic Faraday Effect

The structure and the electrical and magnetic properties of Mn-implanted Si, which exhibits ferromagnetic ordering at room temperature, are studied. Single-crystal n- and p-type Si wafers with high and low electrical resistivities are implanted by manganese ions to a dose of 5 × 1016 cm−2. After implantation and subsequent vacuum annealing at 850°C, the implanted samples are examined by various methods. The Mn impurity that exhibits an electric activity and is incorporated into the Si lattice in interstitial sites is found to account for only a few percent of the total Mn content. The main part of Mn is fixed in Mn15Si26 nanoprecipitates in the Si matrix. The magnetization of implanted Si is found to be independent of the electrical resistivity and the conductivity type of silicon and the type of implanted impurity. The magnetization of implanted Si increases slightly upon short-term postimplantation annealing and disappears completely upon vacuum annealing at 1000°C for 5 h. The Mn impurity in Si is shown to have no significant magnetic moment at room temperature. These results indicate that the room temperature ferromagnetism in Mn-implanted Si is likely to be caused by implantation-induced defects in the silicon lattice rather than by a Mn impurity.

Luminescence induced in diamond by He+ ion implantation into SiC/C composites with an inverse opal structure

The crystal lattice vibrational frequencies in the center of the Brillouin zone have been determined with the Raman spectroscopy method. The lattice vibrational frequencies, the phonon density of states, elastic and piezoelectric moduli, Born dynamic charges, and high-frequency dielectric constant have been calculated using the density functional method. All calculated quantities have been compared to the experimental data. A model of a nonpolar paraelectric phase for this compound, as well as a mechanism of the formation of domain in it, has been proposed. The polarization in the experimentally observed polar phase has been calculated.

Lattice dynamics and ferroelectric instability in ordered and disordered PbSc1/2Ta1/2O3 and PbSc1/2Nb1/2O3 solid solutions

Pseudomorphic Si0.76Ge0.24/Si heterostructures grown by molecular beam epitaxy were implanted with Ge ions at 400 8 Ci n such a way that an ion-damaged region was located below the SiGe/Si interface. The effect of Ge-ion irradiation on strainrelaxation rate and defect structure in the heterostructures was studied by transmission electron microscopy (TEM), X-ray diffraction (XRD), atomic force microscopy (AFM), and low-temperature photoluminescence (PL). It was found that annealing at a temperature as low as 600 8C resulted in very high degree of strain relaxation, while density of threading dislocations was low (B/ 10 5 cm 2 ). The enhanced strain relaxation was attributed to the fact that complexes of point defects produced by the heavy-ion implantation at the elevated temperature acted as nucleation sites for dislocations. The obtained results allowed us to propose a method for preparation of thin highly relaxed SiGe layer with low threading dislocation density and good surface morphology. # 2003 Elsevier Science B.V. All rights reserved.