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In this paper, a series of Yb (0.5mol.%):Ho (0.5mol.%):LiNbO3 crystals doped with various concentration of Mg (1, 3, 5 and 7mol.%) were grown by the Czochralski technique. The ability of optical damage resistance of Mg:Yb:Ho:LiNbO3 crystals increases with increasing the Mg doping concentration. The optical homogeneity of Mg:Yb:Ho:LiNbO3 crystals doped with different concentration of Mg was detected using the birefringence gradient method. The results demonstrated that the optical homogeneity is getting better with the increase of the Mg doping concentration. The studies on the infrared transmission spectra indicated that Mg ions first replaces anti-site Nb in the form of Mg defect, once the concentration of Mg reaches or exceeds the threshold concentration, it begins to substitute Li-site and Nb-site of normal lattice and form defect of Mg3Mg. Therefore, the change of Mg doping concentration is the fundamental reason leading to a violet shift of the OH absorption peak. [ABSTRACT FROM AUTHOR]

Point defect structure of B2 TrSc (TrCd, Ru) alloys was investigated using supercell and special quasi-random structure (SQS) approaches. According to our results, Tr and Sc anti-sites are the constitutional point defects in Tr-rich and Sc-rich B2 TrSc, respectively. To investigate the thermal defect concentrations at finite temperatures, we adopted the Wagner-Schottky model using point defect formation enthalpies obtained from supercell and SQS approaches. The present results suggest that the predominant thermal defects in B2 CdSc are of exchange type, and in B2 RuSc are of interbranch Sc type. The calculated results show an agreement with the available theoretical and experimental data. [ABSTRACT FROM AUTHOR]

In this paper the results of experimental study of microstructure changes in Zr–1Nb alloy after low energy high current pulsed electron beam surface modification and hydrogenation are discussed. Surface treatment was carried out with energy density equal from 5 to 25 J/cm 2 and impulses number equal from 1 to 5. Subsequent hydrogenation was carried out at temperature equal to 350 °C until reaching the hydrogen concentration of 0.05 wt.%. The structure was analyzed by X-ray diffraction, transmission electron microscopy and by means of electron–positron techniques. [ABSTRACT FROM AUTHOR]

The electron paramagnetic resonance (EPR) parameters (g factors gi and the hyperfine structure constants Ai, i = x, y, z) are interpreted by using the perturbation formulae for a 3d9 ion in rhombically (D2h) elongated octahedra. In the calculated formulae, the crystal field parameters are set up from the superposition model, and the contribution to the EPR parameters from the admixture of d-orbitals in the ground state wave function of the Cu2+ ion was taken into account. Based on the calculation, local structural parameters of the impurity Cu2+ center in Cd2(NH4)2(SO4)3 (CAS) crystal were obtained (i.e., Rx ≈ 2.05 Å, Ry ≈ 1.91 Å, Rz ≈ 2.32 Å). The theoretical EPR parameters based on the above Cu2+-O2- bond lengths in CAS crystal show a good agreement with the observed values. The results are discussed. [ABSTRACT FROM AUTHOR]

A unified calculation of optical band positions and electron paramagnetic resonance (EPR) (or spin-Hamiltonian) parameters for the trigonal Cr3+–Li+centre in CsMgCl3crystal is made by using the complete diagonalisation (of energy matrix) method based on the two-spin–orbit-parameter model. In this model, the contributions from the spin–orbit parameter of central dnion and that of ligand ion are included. From the calculation, the 11 observed optical and EPR data (eight optical band positions and three EPR parametersg//,g⊥,D) are reasonably explained with five adjustable parameters and the defect structure of the Cr3+–Li+centre (which is consistent with the expectation based on the electrostatic interaction) in CsMgCl3is acquired. The results are discussed. [ABSTRACT FROM PUBLISHER]

The optical damage resistance ability of the co-doped M:Fe:LiNbO 3 crystals with 0.03 wt% Fe 2 O 3 and various concentration of M (M = Mn, Mg, or Zn,) were measured experimentally. The shift of the fundamental absorption edge as well as the absorption coefficient was obtained in order to investigate their defect structures. A method of confirming the polarization ability dimension of doped ions is brought forward. The indirect transition properties of the fundamental absorption edge below 3.8 eV were investigated experimentally. Possible models to explain the experiments results are discussed. [ABSTRACT FROM AUTHOR]

High-order perturbation formulas for a 3d 9 ion in tetragonally elongated octahedral was applied to calculate the electron paramagnetic resonance (EPR) parameters ( g factors g || , g ⊥ and hyperfine structure constants A || , A ⊥ ) of the tetragonal Cu 2+ center in ZnAl 2 O 4 spinel at the temperature T =4.2 K. In the calculations, the required crystal-field parameters are estimated from the superposition model which enables correlation of the crystal-field parameters and hence the EPR parameters with the tetragonal distortion (characterized by relative tetragonal elongation ratio ρ along the C 4 axis due to the Jahn–Teller effect) of [CuO 6 ] 10− cluster, and the ligand orbital and spin–orbit coupling contributions are included on the basis of the cluster approach in view of moderate covalency for the studied systems. The calculated results show good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

For the first time, the defect structure of mayenite was developed on the basis of conventional Kröger–Vink method and successfully verified using available data on its properties such as total conductivity, hydration/dehydration and oxidation/reduction. As a consequence, equilibrium constants of the quasichemical reactions of mayenite reduction and hydration were determined as a function of temperature. This allowed estimation of Ca 12 Al 14 O 33 − δ enthalpy of reduction and hydration. The former was found to be equal to 360 kJ/mol while the latter was estimated as − 238 kJ/mol. The defect structure model proposed enabled estimation of oxygen nonstoichiometry in mayenite. [ABSTRACT FROM AUTHOR]

X-Ray Absorption Spectroscopy studies of the W (0–1 at% W) and Mo-doped TiO 2 (0–1 at% Mo) nanoparticle specimens at the K edges of titanium and molybdenum as well as at the L 2 L 3 edges of tungsten are presented. The materials were prepared with Flame Spray Synthesis process by oxidation of metal-organic precursors. The Ti:K edge spectra in the XANES range show pre-edge and post-edge features characteristic for anatase. A decrease of the amplitude of the EXAFS function with doping is observed and attributed to a softening of the crystal lattice. The Mo EXAFS functions show a considerable decrease of the second-neighbour-shell peak with increasing Mo content, which is attributed to an increased number of cation vacancies. For tungsten a less pronounced effect is observed. The Mo and W XANES spectra do not show noticeable changes with doping level, which indicates their unchanged oxidation states. [ABSTRACT FROM AUTHOR]

The intrinsic mission in the field of electrical insulation is to make the insulator or the power equipment withstand voltage as high as possible. On one hand, extensive research has focused on improving insulation materials or optimizing the design to endure higher voltage, whereas on the other hand, efforts have addressed the suppression of voltage surges because this indirectly improves the capability of the equipment to withstand higher voltages. ZnO varistors, exhibiting excellent nonlinear I-V characteristics, are specialized in discharging transient surges and limiting the voltage to a magnitude that is not harmful to power equipment. Because of their good price-to-performance ratio, ZnO varistors are the most common overvoltage protection component in AC power protectors. The discovery of the nonlinear I-V characteristics of ZnO ceramics in the 1960s [1] trigged interest in scientific research and industry [2]?[7]. The mysteries about the interfacial states at the grain boundaries and the point defect structures have attracted much attention from theoretical and experimental aspects. As a result, ZnO varistors developed rapidly to meet new challenges from the power system and electronic sectors. ZnO varistors developed rapidly during the past 30 years, not only in China but also in the world, and benefited from the contributions of the universities on the fundamentals and key processing techniques. The objective of this article is to give an overview of the research carried out over the last 30 years that has contributed to the development of ZnO varistors in a broad sense. We emphasize, in our view, the remarkable progress in the fundamental research, which has revealed the physical origin of the obtained properties, the key processing techniques, which have provided important guidance on how to obtain ZnO ceramics with the required performance, and the advanced products now available from industry. [ABSTRACT FROM PUBLISHER]

The spin-Hamiltonian parameters (gfactorsg//,, and hyperfine structure constantsA//,) of the tetragonally compressed Nb4+center in cubic Cs2ZrCl6crystal are calculated from two theoretical methods: one is the complete diagonalization (of energy matrix) method and another is the perturbation theory method. Both methods are based on the two-spin–orbit-parameter model where the contributions to spin-Hamiltonian parameters from the spin–orbit parameter of centraldnion (in the conventional crystal field theory) and that of ligand ion via covalence effect are contained. The calculated results from the two methods are in reasonable agreement with the experimental values. The tetragonal distortion of (NbCl6)2−octahedral cluster due to the Jahn–Teller effect for Nb4+at the cubic Zr4+site in Cs2ZrCl6is also acquired. The results are discussed. [ABSTRACT FROM AUTHOR]

crystals codoped with 0.1 mol% of and three concentrations of (0, 2 and 4 mol%) were grown by the Czochralski method from the congruent melt. The X-ray diffraction (XRD) patterns, UV-visible absorption and infrared (IR) spectra were measured to analyze the crystal composition and defect structure. The blue and green upconversion emissions of ions under 598 nm excitation were observed. The intensity of upconversion emissions was increased by the introduction of 2 mol% zirconium ion and decreased by the introduction of 4 mol% ions. The luminescence decay measurement indicated that the 4G7/2 state of ion was mainly populated by excited state absorption process. It was proposed that crystals doped with approximately 2 mol% ions could be applied as laser materials at 522/535 nm. [ABSTRACT FROM AUTHOR]

• Synthesis catalyst of dispersing CB in AC pores and surface was introduced. • HNO 3 modification and CB loading greatly improve catalytic activity of AC. • Nitrogen and oxygen functional groups benefit methane adsorption. • CB loading increases microcrystalline refinement degree of AC to form micropores. • Protrusion with unique defect structure increases catalytic activity. Catalytic methane decomposition is considered as a promising hydrogen production technology without CO 2 emission. Catalyst is generally required to reduce reaction temperature, among which, carbon-based catalysts are widely studied due to their excellent catalytic performance and low cost. Activated carbon (AC), although presents high initial activity, suffers from fast deactivation; In comparison, carbon black (CB) shows low activity but good stability, and its catalytic performance maintains ability inspires a novel method for AC optimization. According to the physical property difference of AC and CB, a novel catalyst is prepared by doping CB on the surface and in the pores of AC. And surface property modified by HNO 3 is also recommended, because the increase of functional groups further improves the adsorption performance. The results illustrate that AC N + BP2000-20:3 show advantages in hydrogen yield, weight increase velocity and carbon yield. Meanwhile, not only the initial activity is improved by a large margin, but also the deactivation time is progressively prolonged. The analysis results show that CB loading significantly increased the number of micropores, which is the key factor for the high initial catalytic activity. And the protrusion, induced by CB, are characterized by unique graphene edges defect, which provides active sites and furtherly promotes the reaction. [ABSTRACT FROM AUTHOR]

Nonlinear optical properties of lithium niobate crystals doped with alkaline-earth (Zn2+) and rare-earth (Er3+) elements were quantitatively studied from the chemical bond viewpoint of crystal. The different influences of Zn and Er dopants on the dielectric response of LiNbO 3 were compared. The value of nonlinear optical second-harmonic generation coefficients was determined mainly by the Li–O bonds both in LiNbO 3 :Zn and LiNbO 3 :Er crystals. We observed sharp changes in the second order nonlinear optical response of Zn-doped LiNbO 3 single crystals at 1064 nm with increasing Zn concentration in the crystal. The calculated values of the nonlinear optical coefficients for the LiNbO 3 :Zn crystals exceed those for the LiNbO 3 :Er crystals. The LiNbO 3 :Zn crystal with dopant concentration 5.48 mol.% is the most suitable crystal for the second-harmonic conversion. • Nonlinear optical properties of LiNbO 3 :Er and LiNbO 3 :Zn were studied. • Dependences of dij coefficients on the dopant concentration were different for crystals. • Nonlinear optical second-harmonic generation coefficients were determined mainly by Li–O bonds. • The most noticeable changes in d ij coefficients were observed at dopant threshold concentration. • LiNbO 3 :Zn crystals were the most suitable medium for second-harmonic generation. [ABSTRACT FROM AUTHOR]

The effect of thermobaric treatment on the nanoporosity (excess free volume) and thus on the physical and mechanical properties of some amorphous alloys obtained by extra rapid quenching is studied. [ABSTRACT FROM AUTHOR]

In the present investigation, a radically new and simple method of evaluation of the proton conductivity is proposed. This method is based on the conductivity measurement of ceramic materials depending on the oxygen partial pressure (pO 2 ) at a gradual transition from the atmosphere of pure oxygen to one of wet hydrogen: O 2 → O 2 (H 2 O) → H 2 O (O 2 ) → H 2 O → H 2 O (H 2 ) → H 2 (H 2 O). Experimental data of total conductivities for the solid electrolyte BaCe 0.9 Gd 0.1 O 3– δ (BCG) have been fitted with modeling ones in accordance with the defect chemistry model at 600, 750 and 900 °C. Experimental and theoretical relationships correlate well with each other, demonstrating the success of the proposed model description. Analysis of dependences of the total conductivity as a function of pO 2 with simultaneous change of pO 2 and water partial pressure (pH 2 O) allows the estimation of the contribution of the partial conductivities (protonic, oxygen ionic, electronic) in the total one and the identification of the areas of purely ionic and purely protonic conductivity. Using the obtained data, some transport phenomena of proton-conducting materials, which were not previously interpreted, are discussed. [ABSTRACT FROM AUTHOR]

The results of chemical expansion measured as a function of oxygen partial pressure, p O 2, and temperature by means of dilatometric technique are presented for the perovskite-type doped cobaltite La 0.7 Sr 0.3 Co 0.9 Fe 0.1 O 3− δ . The modeling of the defect structure of this perovskite was carried out. Within the framework of the model all iron sites are assumed to be occupied by localized holes whereas both electrons and holes can be localized on cobalt sites in La 0.7 Sr 0.3 Co 0.9 Fe 0.1 O 3− δ . The defect structure model proposed was shown to fit perfectly well available experimental data on oxygen nonstoichiometry of the perovskite studied. Equilibrium constants of the appropriate defects reactions were, therefore, determined and concentrations of all defect species defined within the framework of the model proposed were calculated as functions of temperature and oxygen nonstoichiometry. These concentrations were employed in the chemical expansion model derived by us earlier in order to compute the chemical expansion of the La 0.7 Sr 0.3 Co 0.9 Fe 0.1 O 3− δ lattice as a function of its oxygen nonstoichiometry. Cobalt ions transition from low spin (LS) state to high spin (HS) one induced by temperature increase was taken into account as well. The model proposed was shown to coincide completely with experimental data on chemical expansion for the La 0.7 Sr 0.3 Co 0.9 Fe 0.1 O 3− δ at all temperatures investigated. As a result, the spin state distribution of cobalt was calculated depending on temperature for the oxide studied. [ABSTRACT FROM AUTHOR]

Atomic structure and localized vibrations of α-SiO 2 :Ge was studied using computer modeling techniques. The simulation was carried out by the lattice dynamics calculation of the symmetrized local density of vibrational states. The modeling is based upon a Buckingham type potential. Calculations of the equilibrium structure were done with a lattice energy minimization code. Frequencies of localized symmetrized vibrations induced by Ge impurities are identified. The movements of atoms located near Ge impurity are analyzed and their contribution into localized vibrations of different type is evaluated. [ABSTRACT FROM AUTHOR]

Bismuth and niobium co-substitutions on lanthanum molybdate with the nominal formula La 2− x Bi x Mo 2− x Nb x O 9− δ ( x = 0–0.24) (LBMN) are synthesized via solid state reaction. Their structures and properties are studied by powder X -ray diffraction (XRD), thermal analysis, electron diffraction, and impedance spectroscopy. XRD experiments and thermal analysis demonstrate the stabilization of the high temperature cubic phase when x ≥ 0.04. Studies of the polar area in electron diffraction confirm the inhomogeneous nature of the composition. A modified Debye relaxation approach is employed to learn the ion dynamics, and it shows non-monotonic functions in relaxation parameters τ 0 and the activation energy E a , which is in agreement with the volume variation of the basic [O1La3Mo] tetrahedral as a new structural description. As a result, the LBMN system exhibits good performance in electrical conductivities at high temperature, and shows a decrease of the average thermal expansion coefficients (TECs) along the dopant content. [ABSTRACT FROM AUTHOR]

Abstract: Thermally stimulated depolarization current (TSDC) measurements were performed on 3mol% and 8mol% yttria stabilized zirconia ceramics (3YSZ and 8YSZ), in order to observe defect associations. Several TSDC peaks were observed, and the characteristics suggested that the peaks were attributed to space charge polarization due to long range migration of oxygen vacancies and electric dipole polarization due to trimeric defect association of Y at Zr site (YZr') and oxygen vacancy (Vö). The activation energies for the dipole polarizations were different between 3YSZ and 8YSZ. The difference was caused by the difference of the structure of defect association. In addition, in 3YSZ, peaks with high activation energy of 1.24eV were observed. The high activation energy suggests the presence of oxygen migration across Y–Y edges, in other word, indicating that Y–Y pairs exist in 3YSZ. [Copyright &y& Elsevier]

Abstract: Optical spectroscopy data has been collected on the energy needed for electron transfer from the valence band to Ti4+ in about 40 different insulating and II–VI and III–V semiconducting compounds. It provides a measure for the location of the Ti3+ 3d1 ground state level above the valence band. This is combined with the vacuum referred binding energy (VRBE) of valence band electrons as obtained with the chemical shift model based on lanthanide impurity spectroscopy. It provides the VRBE of an electron in the Ti3+ ground state level. This work will first show that the energy of electron transfer to Ti4+ is about the same as that to Eu3+ irrespective of the type of compound. Next it will be shown that the VRBE of the Ti3+ 3d1 ground state is always near −4eV. An approximately ±1eV spread around that value is attributed to the crystal field splitting of the Ti3+ 3d-levels. [Copyright &y& Elsevier]

The electron paramagnetic resonance (EPR) parameters (gfactorsgxx,gyy,gzzand hyperfine structure constantsAxx,Ayy,Azz) are interpreted by taking account of the admixture of d-orbitals in the ground state wave function of the Cu2+ion in a Zn(C3H3O4)2(H2O)2(DABMZ) single crystal. Based on the calculation, local structural parameters of the impurity Cu2+center were obtained (i.e. Ra≈1.92 Å,Rb≈1.96 Å,Rc≈1.99 Å). The theoretical EPR parameters based on the above Cu2+−O2−bond lengths in the DABMZ crystal show good agreement with the observed values and some improvements have been made as compared with those in the previous studies. [ABSTRACT FROM AUTHOR]

Abstract: The 45×45 complete energy matrix for 3d8 ion at D2h site symmetry is used to calculate and assign the ground-state splitting and the fine structure of the multiplets of Ni2+(3d8) doped in MgF2 crystal with rutile type structure by the complete diagonalizaton method (CDM) in the frame of semi-empirical molecular orbital (MO) scheme in the strong crystal field (CF) approximation. In the calculation, all the configuration interactions though the cubic CF part, low-symmetry component (tetragonal and orthorhombic parts), Coulomb interaction and the spin–orbit coupling (SOC) interaction (both of the central ion and the liangds) are taken into account completely. The calculated results are in good agreement with the experimental data. In addition, the ground-state splitting is also calculated by the high-order perturbation method (PTM), together with the electron paramagnetic resonance (EPR) parameters D, E and g-factors (g x , g y and g z ). The results of the spin–orbit splitting of the ground state calculated by CDM and PTM are not only close to each other, but also in good agreement with the observed data. The relationship between crystalline parameters and the fine structure of multiplets and EPR spectrum is established and the local defect structure is determined. [Copyright &y& Elsevier]

The eight optical spectral band positions and three spin-Hamiltonian parameters (gfactorsg//,g⊥and zero-field splittingD) of V2+ions in trigonal CdCl2crystal are calculated together from the complete diagonalisation (of energy matrix) method (CDM) based on the two-spin-orbit-parameter model (also called the cluster approach). In the model, differing from the usual one-spin-orbit-parameter model in the conventional crystal-field theory (where only the contribution to spin-Hamiltonian parameters due to the spin-orbit parameter of centraldnion is considered), both the contributions from the spin-orbit parameter of centraldnion and that of ligand ions are taken into account. The calculated results show reasonable agreement with the experimental values. The local lattice relaxation in the vicinity of V2+ion due to the introduction of V2+impurity is acquired from the calculations. The calculations of spin-Hamiltonian parameters from the CDM based on the one-spin-orbit-parameter and those from the perturbation theory method based on the two-spin-orbit-parameter model are also made for comparison. The results are discussed. [ABSTRACT FROM AUTHOR]

A novel method, gas–liquid phase chemical deposition is developed to prepare In2S3 and In2S3:Ce nanoparticles. The structural, morphology and composition feature of these two nanoparticles is studied by XRD, HRTEM, and XPS. In situ high-pressure synchrotron X-ray diffraction studies were carried out by using a diamond-anvil cell. The doping does not influence the tetragonal-to-cubic phase transition path while results in a lower phase transition pressure of In2S3:Ce nanoparticles (4.3GPa) than that of In2S3 nanoparticles (7.1GPa). The bulk moduli of tetragonal phases are B 0=87.1±4.3GPa and B 0=55.6±4.1GPa, respectively. The distinct high-pressure behaviors can be explained in term of the doped ions, causing lattice distortion and reducing structural stability of the In2S3 nanoparticles and further accelerating the phase transition. [ABSTRACT FROM AUTHOR]

Abstract: The spin-Hamiltonian parameters (g factors g ‖, g ⊥ and hyperfine structure constants A ‖, A ⊥) of the tetragonal Mo5+ center in reduced BaTiO3:Mo crystal with low temperature phase are calculated from the high-order perturbation formulas based on the two-mechanism model for d1 ions in octahedral clusters with the ground state 2 B 2 (|d xy 〉). In the model, both the contributions to spin-Hamiltonian parameters from the crystal-field (CF) mechanism and that from the charge-transfer (CT) mechanism (which is neglected in the widely-used crystal field theory) are considered. The calculated results are in reasonably agreement with the experimental values. The calculations show that for the spin-Hamiltonian parameters of BaTiO3:Mo5+, the relative importances of CT mechanism |Q CT/Q CF| are about 17%, 9%, 7% and 7% for Q=Δg ‖, Δg ⊥, , and (where Δg=g−g e , g e ≈2.0023, the g factor of free electron), respectively. It appears that for the high valence state d n ion clusters in crystals, the precise and complete calculations of spin-Hamiltonian parameters should take both the CF and CT mechanisms into account. The tetragonally-compressed distortion of (MoO6)7− octahedral clusters in the low-temperature rhombohedral phase of BaTiO3 caused by the static Jahn–Teller effect is also acquired from the calculations. The results are discussed. [Copyright &y& Elsevier]

Abstract: Spatially resolved X-ray diffraction techniques provide useful quantitative information on the defect structure distribution for single crystals, thin films or nanowires. In this study, high-resolution X-ray diffraction is used at a laboratory X-ray source, to study the defect structure of undoped and Yb doped needle-shaped PrVO4 crystals grown by the slow cooling method, and to observe the effect of Yb doping on crystal structure and quality. General information on the defect structure is derived from reciprocal lattice-point maps at several selected points. Details of the defect structure are obtained with the use of mapping of triple axis rocking curves and of 2θ/ω diffraction curves. Combining these techniques provided useful information on the variation of defect nature and distribution along the crystals. There is no particular difference between the undoped and doped crystals. They are typically single crystalline, some of them are built from several blocks with misorientation angles up to several hundred arcsec. The full width at half maximum (FWHM) at the central part of the crystals is as low as about 10–12arcsec. There is a tendency of FWHM to increase close to the crystal tips, demonstrating that the crystals are of lower crystalline quality at these regions. The mappings performed for (100) and (010) faces show that one of faces exhibits a small curvature (the lattice tilt being smaller than 2arcsec/mm), whereas the other is characterized by a larger curvature (the tilt by at least three times larger). Unexpectedly, the reciprocal lattice-point maps for (100) and (010) crystal faces include an additional reciprocal lattice point of weak intensity. Its possible origin is discussed. [Copyright &y& Elsevier]

Abstract: The spin-Hamiltonian (SH) parameters (g factors g // , g ⊥ and hyperfine structure constants A //, A ⊥ ) of K2SnCl6: Mo5+ (4d 1) crystal are theoretically studied by the use of two microscopic spin-Hamiltonian (SH) methods, the high-order perturbation theory method (PTM) and the complete diagonalization (of energy matrix) method (CDM) within the molecular orbital (MO) scheme. The contributions arising both from the crystal field and charge transfer excitations are taken into account. The investigations show that the charge transfer mechanism plays a decisive role in the understanding of the spin-Hamiltonian (SH) parameters for 4d 1 ions in crystals with the strong coordinate covalence, especially for g // >g ⊥ which cannot be explained in the frame work of traditional crystal field approximation (CFA). The local defect structure around Mo5+ impurity ion center is determined to be D 4 h point group symmetry. [Copyright &y& Elsevier]

Abstract: Zr:Fe:LiNbO3 crystals were grown in air by the Czochralski technique with various [Li]/[Nb] ratios of 0.85, 1.05, and 1.38 in melt. Based on the ICP-AES (inductively coupled plasma atomic emission spectrometry) analyzed results, the chemical formulas of Zr:Fe:LiNbO3 crystals were obtained. The sign of the dominate charge carriers as well as the two-wave coupling gain coefficient as a function of the [Li]/[Nb] ratios in crystal were investigated by using the typical two-wave coupling experimental setup. The results show that electrons are the dominate charge carriers and the gain coefficient is the largest when the recording angle 2θ=21° in the sample with [Li]/[Nb]=0.7111 in crystal. In addition, the dependence of the light-induced birefringence on the [Li]/[Nb] ratios was measured in Zr:Fe:LiNbO3 crystals, which shows that the optical damage resistance of Zr:Fe:LiNbO3 crystals increases with the increasing of [Li]/[Nb] ratios at 532nm wavelength. The dependences of the green photorefraction on the defect structure of Zr:Fe:LiNbO3 crystals are discussed in detail based on the obtained chemical formulas. [Copyright &y& Elsevier]

Transmission electron microscopy permits quantitative analysis of how the phase composition and defect substructure in the surface layer of rail steel consisting of plate pearlite and martensite nanozones evolve under fatigue. The fatigue failure of rail steel with different structures is discussed. [ABSTRACT FROM AUTHOR]

The paper presents the results of the ZnO nanopowder modification investigation by means of laser shock-wave treatment. The peculiar effects of such treatment were studied at the energy density rate of ∼108-109 W/cm2. The ZnO nanopowder properties were explored by using such methods as X-ray diffraction analysis (XRD), scanning electron microscopy and also by photoluminescence spectra decomposition analysis. The XRD study of ZnO nanopowder sample revealed its crystalline structure with the typical hexagonal wurtzite phase. It was also proved that laser shock-wave treatment allows to essentially changing the aggregation level of nanopowder. Additionally, the photoluminescence spectra changes of ZnO naopowders were explored both under air ambient and vacuum for the initial and laser shock-wave treated nanopowder. The decreasing intensity of green photoluminescence band and increasing intensity of the peak λ =430 nm was observed when ambient air pressure decreases. The registered changes of visible emission are referred to the modification of defect structure, especially oxygen defects. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Highlights: [•] Spin-Hamiltonian parameters of two tetragonal Gd3+ centers in Tl2ZnF4 are calculated. [•] The calculation are made using the diagonalization method. [•] This diagonalization method is based on one-electron crystal field mechanism. [•] Defect models of both Gd3+ centers are confirmed and defect structures are obtained. [Copyright &y& Elsevier]

Ferroelectric oxides are used in a large variety of modern technologies including sensors, transducers, actuators, thin film memories and energy harvesting devices. In that respect, one strategy to obtain tailored materials properties for a specific application is provided by systematically modifying the defect structure in terms of either aliovalent doping or non-stoichiometry. Recent advances in spectroscopic characterisation techniques combined with ab initio calculations have significantly contributed to the understanding of how defects impact the materials properties. This review provides an overview of recent results and lists still open questions to be addressed in future work. [ABSTRACT FROM AUTHOR]

The microstructure and defect structure of low-carbon steel after equal-channel angular pressing and electroplastic rolling are considered. The influence of such treatment on the microhardness and impact strength of steel is established. [ABSTRACT FROM AUTHOR]

Abstract: The g factors g  and g ⊥ for the tetragonal (SmF12)9− cluster due to Sm3+ occupying the 12-fold coordinated K+ site in KMgF3 perovskite are calculated from a diagonalization (of energy matrix) method. In the energy matrix, the crystal field parameters used are calculated from the superposition model with the intrinsic parameters close to those of (GdF12)9− clusters for Gd3+ in similar cubic perovskite c-RbZnF3. In the calculations, the applied defect model of tetragonal Sm3+ center in KMgF3 is that in which Sm3+ occupies the 12-fold coordinated K+ site associated with one (model A) or two (model B, where two K+ vacancies are at both sides of Sm3+) nearest K+ vacancies along the C 4 axis for partial or complete charge compensation. The calculation results reveal that when the calculated g  and g ⊥ are in reasonable agreement with the experimental values, the tetragonal distortions of Sm3+ centers are, whether in model A or model B, very small because of the slight anisotropy of the observed g factors. So, we suggest that the defect model of Sm3+ center is that in which Sm3+ occupies the 12-fold coordinated K+ site associated with one or two next-nearest rather than nearest K+ vacancies along the C 4 axis to result in small tetragonal distortions and hence in the small anisotropy of g factors. The reasonableness of our suggested defect model is discussed. [Copyright &y& Elsevier]

The effects of fast and slow dynamics in acoustic resonators from rock and metal samples from the D16 microcrystalline aluminum alloy are studied using resonance ultrasonic spectroscopy. Before the experiment, residual shear strains were artificially created in the metal samples. A decrease in the elasticity modulus in the fast dynamics process has been revealed in resonators from rock and the D16 alloy with residual strains. Based on an analysis of the experimental results, the following conclusion was drawn: the experimentally observed slow dynamics effect cannot be explained by thermoelastic effects alone. The slow dynamics effect is to a great extent related to metastable states of the defect structure the latter passes through to due to the force action (dynamic or static) applied to the sample. After its removal, the defect structure slowly relaxes to its equilibrium state. [ABSTRACT FROM AUTHOR]

Highlights: [•] Eu3+-doped cubic Ba3Y2WO9 phosphors were firstly synthesized by sol–gel method. [•] The luminescence excitation and emission spectra were discussed in details. [•] The crystallographic occupations of Eu3+ ions in cubic Ba3Y2WO9 were explored. [Copyright &y& Elsevier]

Highlights: [•] Vibrations of O vacancies in different charged states in α-GeO2 were studied. [•] We estimated the influence of the charge state on the structure and the phonon spectrum. [•] The values of frequencies of vibrations induced by vacancies were calculated. [Copyright &y& Elsevier]

Abstract: High-pressure behaviors of AlN:Mg and AlN:Co nanowires have been investigated by in situ angle dispersive synchrotron X-ray diffraction up to 41.5GPa and 38.2GPa, respectively. Their corresponding pressure-induced wurtzite-to-rocksalt phase transitions start at 17.7GPa and 15.0GPa and complete at 33.2GPa and 31.0GPa, respectively. The phase-transition routes are not affected by the doped ions, while the phase transition pressures are lower than that of pure AlN nanowires. The distinct high-pressure behaviors are ascribed to the doped ions, which reduce the formation energy of cation vacancies and induce Al vacancies defects together with substitution defects, resulting in lattice distortion and affecting structural stability and phase transition pressure. [Copyright &y& Elsevier]