Infrared reflectivity spectrum of KTiOPO4 single crystal

The kinetic theory of overlapping phase transformations is a valuable tool in the characterization of diffusion-controlled precipitation reactions. Using this approach, one can obtain the kinetic parameters (n,?k) for simultaneous diffusion-controlled precipitation reactions, based on the knowledge of a specific macroscopic parameter, P(t), chosen to study the ongoing reaction. Both large and small process overlaps are considered. This methodology calculates the kinetic parameters for defined intervals of the fraction-transformed curve rather than for the entire curve. The approach used in this study permits an evaluation of which are the best protocols for the precipitate nucleation and growth rates during tempering reactions in low-alloy steel, whereas an analysis of the total combined transformations data set could lead to erroneous conclusions.     

V centers in single crystal Al2O3

From optical and thermal bleaching experiments it is concluded that the 400 nm absorption band which appears in Al₂O₃ after γ-irradiation is a composite V band. One of its components is attributed to the V^-_OH center which also is responsible for a localized vibrational band at 3316 cm^-11 analogous to the one observed for the V_OH center in MgO. The irradiation also results in electron trapping at Cr³⁺ impurity ions to produce a band at 227 nm. Annealing at 170°C destroys the V^-_OH center by releasing holes which convert the Cr²⁺ to Cr³⁺ with an attendant thermoluminescence.     

Energy spectrum of electron trapping centers in CuInAsS<Subscript>3</Subscript>

This paper presents the results of the investigation of the energy spectrum of electronic states due to trapping centers, the role of which in CuInAsS₃ is played by lattice defects. The results of the analysis of the thermally stimulated current curves of CuInAsS₃ demonstrate that the energy spectrum of trapping centers is localized under the bottom of the conduction band in the energy range E _C–(0.14–0.35) eV.     

Disorientation kinetics of the B 80 4 centers in single crystal silicon

Using exciton spectroscopy methods, it was established that ₈₀ ⁴ centers can be oriented under uniaxial compression conditions not only in the [111] axis direction, but in the $[\bar 111]$ and $[1\bar 11]$ directions as well. Disorientation of the ₈₀ ⁴ centers was studied in detail, a kinetic equation adequately describing this process is presented, and an expression for the characteristic reorientation time as a function of the temperature was obtained. It was found that the reorientation rate obeys the Arrhenius law with an activation energy of about 1.54 eV. The experimental results are explained proceeding from a hypothesis that the ₈₀ ⁴ center is identical to a ring hexavacancy. A mechanism of the ₈₀ ⁴ center (hexavacancy) reorientation is proposed within the framework of this model, according to which the hexavacancies are thermally excited into the first metastable state and then pass to a ring state with different orientation. Involving the spatial displacement of hexavacancies during reorientation, this process has to be accompanied by the Brownian motion of the hexavacancies. A correlation was found between the direction of orientation of the ₈₀ ⁴ centers (hexavacancies) and the relative change in the 〈11〉bond length under uniaxial compression conditions. This result is interpreted in terms of the hexavacancy geometry.     

Local charge-carrier trapping centers in C60 single crystals

The energy spectrum of local charge-carrier trapping centers in C₆₀ single crystals is studied in terms of the theory of space-charge-limited currents in the Gaussian approximation. The energy distribution of these centers in the energy gap is found, and the type and parameters of this distribution are determined.     

Photoluminescence in YbGa2Se4 and YbGa2Se4:Nd3+ single crystals

The excitation and photoluminescence spectra of YbGa₂Se₄ and YbGa₂Se₄:Nd³⁺ single crystals recorded at different temperatures and neodymium concentrations have been investigated. The photoluminescence spectrum exhibits intracenter luminescence lines of the Nd³⁺ ion in wavelength ranges of 0.804?C0.84, 0.88?C0.92, 0.96?C0.996, and 1.06?C1.12 ??m against a broadband emission background. These ranges are related, respectively, to the ⁴ F _5/2-⁴ I _9/2, ⁴ F _3/2-⁴ I _9/2, ⁴ F _5/2-⁴ I _11/2, and ⁴ F _3/2-⁴ I _11/2 transitions.     

Magnetic resonant mode in the low-energy spin-excitation spectrum of superconducting Rb2Fe4Se5 single crystals

We have studied the low-energy spin-excitation spectrum of the single-crystalline Rb(2)Fe(4)Se(5) superconductor (T(c)=32 K) by means of inelastic neutron scattering. In the superconducting state, we observe a magnetic resonant mode centered at an energy of ?ω(res)=14 meV and at the (0.5 0.25 0.5) wave vector (unfolded Fe-sublattice notation), which differs from the ones characterizing magnetic resonant modes in other iron-based superconductors. Our finding suggests that the 245-iron selenides are unconventional superconductors with a sign-changing order parameter, in which bulk superconductivity coexists with the √5×√5 magnetic superstructure. The estimated ratios of ?ω(res)/k(B)T(c)≈5.1±0.4 and ?ω(res)/2Δ≈0.7±0.1, where Δ is the superconducting gap, indicate moderate pairing strength in this compound, similar to that in optimally doped 1111 and 122 pnictides.     

Trapping centers and their distribution in Tl2In2Se3S layered single crystals

Thermally stimulated current (TSC) measurements have been carried out on Tl₂In₂Se₃S layered single crystals in the temperature range of 10–175 K. The TSC spectra reveal the presence of two peaks (A and B). The electronic traps’ distributions have been analyzed by different light illumination temperature techniques. It was revealed that the obtained traps’ distribution can be described as an exponential one. The variations of one order of magnitude in the traps’ density for every 30 meV (A peak) and 59 meV (B peak) were estimated. Moreover, the mean activation energy, attempt-to-escape frequency, capture cross section and concentration of the traps were determined.     

Optical absorption spectrum of Co2+ in ammonium perchlorate single crystal

Single crystals of cobalt — doped ammonium perchlorate were grown at room temperature. The electronic absorption bands observed at room and liquid air temperatures have been assigned transitions from the ground⁴T₁(F) state to the excited⁴T₂(F),⁴A₂(F),²T₁(G) and⁴T₁(P) states. The crystal parameters derived areDq=880 cm^–1,B=865 cm^–1 andC= 4·63B.The authors wish to express their thanks to the authorities of the Indian Institute of Science, Bangalore for kind permission to use their spectrophotometer. Two of the authors (B. C. V.Reddy and J. L.Rao) express their greatful thanks to the council of scientific and Industrial Research (New Delhi) for financial assistance.     

EPR spectra of Fe centers in layered TlGaSe2 single crystal

A single-crystal TlGaSe₂ doped by paramagnetic Fe ions has been studied at room temperature by electron paramagnetic resonance (EPR) technique. The fine structure of EPR spectra of paramagnetic Fe³⁺ ions was observed. The spectra were interpreted to correspond to the transitions among spin multiplet (S=5/2, L=0) of Fe³⁺ ion, which are splitted by the local ligand crystal field (CF) of orthorhombic symmetry. Four equivalent Fe³⁺ centers have been observed in the EPR spectra and the local symmetry of crystal field at the Fe³⁺ site and CF parameters were determined. Experimental results indicate that the Fe ions substitute Ga at the center of GaSe₄ tetrahedrons, and the rhombic distortion of the CF is caused by the Tl ions located in the trigonal cavities between the tetrahedral complexes.     

Antiferromagnetic resonance in CuB2O4 single crystal

The frequency-field, temperature, and angular dependences of the antiferromagnetic resonance parameters for the tetragonal CuB₂O₄ single crystal are studied in the frequency range 2.6–80 GHz and at temperatures of 4.2–30 K. The results obtained confirm the fact that, in the high-temperature state in the range 10–21 K, this compound is an easy-plane weak ferromagnet. The temperature dependence of the Dzyaloshinski field is determined. An abrupt change observed in the frequency-field dependence of the magnetic resonance at T=4.2 K and H ⊥ C ₄ indicates the transition to the weak ferromagnetic state induced by the external field H _⊥. The phase diagram for CuB₂O₄ is constructed on the H _⊥-T coordinates. It is demonstrated that, in the low-temperature state, the magnetic moments of copper ions remain in the basal plane, but the weak ferromagnetism is absent.     

Electronic absorption spectrum of Ni2+ in lithium potassium sulphate single crystal

Single crystals of nickel-doped lithium potassium sulphate were grown by slow evaporation method at room temperature. From the nature and position of the bands observed, a successful interpretation of all the bands could be made assumingO _h symmetry for the Ni²⁺ ion in the crystal. The bands have been assigned transitions from the ground³A_2g(F) state to the excited³T_2g(F),¹E_g(D),³T_1g(F),¹T_2g(D) and³T_1g(P) states. The crystal field parameters derived areDq=910cm^–1,B=890cm^–1 andC=3560cm^–1.The authors wish to express their thanks to Prof. K. Sreerama Murthy for his constant encouragement throughout this investigation. The authors are also thankful to Prof. Mihir Chowdhury, Indian Association for the cultivation of Science, Calcutta for giving permission to take the spectra.     

Magnetization reversal of CuyCr2Se4−zBrx single crystals

Due to a partially inhomogeneous Cu concentration, Cu_yCr₂Se_4?zBr_x single crystal can show a complicated temperature dependence of the wall motion threshold field which is about 0.5 kA/m near the Curie temperature. The crystals can be homogenized by means of a NH₄OH treatment.     

Energy band structure of CdCr2Se4 by APW method

The results of the first band structure calculation of the CdCr₂Se₄ magnetic semiconductor are reported and discussed in connection with the experiment and band structure results for related nonmagnetic compounds. For the calculation, the unsymmetrized APW method has been chosen due to complexity of the problem as well as physical reasons.     

Ab initio Calculations of Phonon Dispersion in CdGa2S4

Physics of the Solid State - Abstract—The phonon spectrum of CdGa2S4 has been experimentally investigated by Raman spectroscopy and theoretically analyzed using the density functional theory...     

The vibration spectrum and high temperature phase transition of NaBF_4 single crystal

The polarized Raman spectrum of NaBF_4 single crystal measured by use of different geometric arrangements are reported. The obvious anisotropy of the crystal results in the degradation of degenerated modes of BF_4. Experiments show that the vibration frequencies decrease with the increasing of temperature. But when it above the phase transition point the v_1 symmetric stretching vibration is restored. From this, the phase transition temperature can be estimated to be 250℃ (523K).     

Fast intrinsic emission in Cs2CdI4 single crystal

The spectral-luminescent studies of the ${\mathrm{Cs}}_2{\mathrm{CdI}}_4$ single crystals are reported. The fast luminescence in the 3.6–2.0 eV energy range with decay time $\tau =4.6\mathrm{ns}$ was revealed in the crystal under high-energy excitation $(E_{\mathrm{exc}}>8\mathrm{eV})$ at 9 K. This luminescence is supposed to be caused by the hole transitions between subbands of the split valence band. The energy-band picture for ${\mathrm{Cs}}_2{\mathrm{CdI}}_4$ crystals was calculated as a proof of the luminescence model.