Explanations of the optical absorption and ESR spectrum for tetragonal Ni+ centers in CuAlS2:Ni+ crystals

In this paper, the optical absorption and electron spin resonance (ESR) spectrum of Ni⁺‐doped CuAlS₂ crystals have been studied by using a double spin‐orbit (SO) coupling approximation model, where the effects due to the SO coupling of the central metal 3d¹ ion and those of ligands are included. From this model, the formulas of the ESR g factors g_‖, g_⊥ and hyperfine structure constants A_‖, A_⊥ for 3d¹ ions in the tetragonal MX₄ clusters are constructed. The optical absorption and ESR parameters for Cu⁺ sites of CuAlS₂ have been calculated. The results obtained show that Ni⁺ ions substitute for Cu⁺ ions sites. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigations of spin‐Hamiltonian parameters and defect structures for two tetragonal Cu2+ centers in KTaO3 crystal

Based on the defect models that the two tetragonal Cu²⁺ centers in KTaO₃ are due to Cu²⁺ ions at Ta⁵⁺ sites associated, respectively, with one and two oxygen vacancies (V₀) along C₄ axis because of charge compensation, the spin‐Hamiltonian parameters (g factors g_‖, g_⊥and hyperfine structure constants A_‖, A_⊥) of both Cu²⁺ centers in KTaO₃ are calculated from the perturbation theory method (PTM) and the complete diagonalization (of energy matrix) method (CDM). The calculated results from both theoretical methods are not only close to each other, but also in reasonable agreement with the experimental values. This suggests that both methods are effective in the explanations of spin‐Hamiltonian parameters for 3d⁹ ions in tetragonal symmetry. From the calculations, the defect models are confirmed and the defect structural data are obtained for both Cu²⁺ centers in KTaO₃. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spin‐Hamiltonian parameters for Dy3+ ion at the trigonal 12‐fold coordinated La3+ site of La2Mg3(NO3)12·24H2O

The spin‐Hamiltonian parameters (g factors g_‖, g_⊥ and hyperfine structure constants ¹⁶¹A_‖, ¹⁶¹A_⊥, ¹⁶³A_‖, ¹⁶³A_⊥) for ¹⁶¹Dy³⁺ and ¹⁶¹Dy³⁺ isotopes in the trigonal 12‐fold coordinated La³⁺ site of La₂Mg₃(NO₃)₁₂·24H₂O crystal are calculated from a diagonalization (of energy matrix) method. In the method, the Zeeman and hyperfine interaction terms are added to the conventional Hamiltonian used in the studies of crystal‐field energy levels, and a 66×66 energy matrix concerning the ground multiplet ⁶H_15/2 and the first to fifth excited multiplets ⁶H_13/2, ⁶H_11/2, ⁶H_9/2, ⁶H_7/2 and ⁶H_5/2 are applied. The calculated results are discussed. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

An EPR Study of Scapolite

In single crystals of scapolite from two different localities, three paramagnetic centres are detected by electron paramagnetic resonance (EPR): 1. One isotropic singlet with g_iso = 2.005; 2. One triclinic singlet with g‖ = 2.005 ± 0.001 and g⟂= 2.009; 3. One triclinic sextet with g‖= 2.005 ± 0.001, g⟂ = 2.011; A‖ = 85.4 × 10⁻⁴ cm⁻⁴, A⟂ = 85.3 × 10⁻⁴ cm⁻¹. Centres 1 and 2 can be attributed to colour centres as they are bleached after annealing. Centre 3 can be due to Mn²⁺ (only the central M_s = ± 1/2 transition is observable) most likely substituting for Ca²⁺ The site symmetry must be triclinic but due to Al, Si disorder and mixed Na, Ca composition the different components from magnetically non-equivalent sites are averaged out for many orientations.     

Theoretical studies of the spin Hamiltonian parameters and the local structures for the tetragonal Cu centers in the LKB glasses

The spin Hamiltonian parameters (g factors g_∥, g_⊥ and the hyperfine structure constants A_∥, A_⊥) for the Cu²⁺ centers in the lithium potassium borate (LKB) glasses xLi₂O·(30 − x)·K₂O·70B₂O₃ (0 ≤ x ≤ 25) were theoretically studied using the high-order perturbation formulas of these parameters for a 3d⁹ ion in a tetragonally elongated octahedron. The [CuO₆]¹⁰⁻ clusters in the LKB glasses are found to suffer the relative elongations of about 3% along the tetragonal axis due to the Jahn-Teller effect. The concentration dependences of the g factors are illustrated by the approximately linear decrease of the cubic field parameter Dq as well as the increases of the covalency factor N and the relative elongation ratio ρ due to the slight expansion of the cell volume or bond lengths with increasing the Li₂O concentration x. Meanwhile, the slow non-linear increases of the hyperfine structure constants are described as the rough exponential increase of the core polarization constant κ with x due to the increase of the tetragonality of the systems. The theoretical spin Hamiltonian parameters and their concentration dependences show good agreement with the experimental data. To evaluate validity and applicability of the present theoretical model and formulas, the EPR results of the Cu²⁺ centers in similar lithium sodium borate (LNB) xLi₂O·(30 − x)·Na₂O·70B₂O₃ (5 ≤ x ≤ 25 mol%) glasses are also analyzed and compared with those in the LKB systems using the uniform model and formulas.     

Structural characterization and magnetic properties of the spinel compound CoIn0.5Cr1.5S4

Single crystals of the magnetic semiconductor CoIn_0.5Cr_1.5S₄, belong to the system CoIn_(2‐2X)Cr_(2X)S₄ with x = 0.75, was grown by the chemical transport method. X‐ray powder diffraction characterization by the Rietveld method indicated that CoIn_0.5Cr_1.5S₄ crystallizes in the space group Fd‐3m, Z = 8, with a = 10.0700(6) Å and V = 1021.2(1) ų, in a normal spinel structure. The temperature dependence of the DC magnetization suggests that the studied compound presents a ferromagnetic behavior with a Curie temperature Tc = 220 K. Sharp spin‐glass like behavior was found also. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The crystal and molecular structures of formyl-, cyano-, and amino-cyclopentadienyldicarbonylnitrosylchromium

The x-ray crystallographic structures of ( ⁵-C₅H₄CHO)Cr(CO)₂NO (I), ( ⁵-C₅H₄CN)Cr(CO)₂NO (II), and ( ⁵-C₅H₄NH₂)Cr(CO)₂NO (III) are described. The formyl and amino derivatives were obtained from a literature preparation (Macomber and Rausch, 1983). The cyano derivative (II) was obtained by conversion of ( ⁵-C₅H₄COOH)Cr(CO)₂NO into [( ⁵-C₅H₄C(O)NH₂]Cr(CO)₂NO, followed by dehydration of the amide in acetic anhydride. (I) crystallizes in the monoclinic space groupP2₁/n witha=8.028(3),b=11.605(4),c=9.730(3)Å,=90.04(2)°, andD _calc=1.69 g cm^–3 forZ=4. Refinement led to anR value of 0.031 based on 1279 observed reflections ([I>-3(I)]). (II) belongs to the triclinicP¯1 witha=6.838(3),b=6.879(3),c=10.130(3)Å,=92.23(2),=92.98(2), =107.65(3)°, andD _calc=1.67 g cm^–3 forZ=2. Refinement gaveR=0.042 for 1543 observed reflections. (III) was found to be orthorhombicPbca witha=7.259(3),b=13.449(3),c=18.090(5)Å, andD _calc=1.64 g cmsu–3 forZ=8. Refinement producedR=0.026 for 767 observed reflections. In (I) the electron-withdrawing formyl group is foundtrans to the nitrosyl. The same holds for the cyano group in (II), but the amino function in (III) is nottrans to any of the tripod ligands.     

Structural,Morphological and Electrical Studies on Barium Strontium Titanate Thin Films Prepared by Sol‐Gel Technique

The crystal structure, surface morphology, compositional homogeneity and electrical properties of barium strontium titanate (BST) thin films are investigated. The films were deposited on bare silicon and platinum coated silicon substrates by spin coating process. The precursor solution with Ba/Sr ratio 70/30 was prepared by sol‐gel synthesis using metal alkoxides. The crystalline nature and morphology of the films are found to be strongly influenced by the heating cycle adopted to form the Ba_0.7Sr_0.3TiO₃ layer. The elemental composition analysis on the surface and in‐depth confirms the stoichiometry of the films. The dielectric constant at 100 kHz and dissipation factor at room temperature is found to be 120 and 0.0236 for the films with 400nm thickness annealed at 700°C for 2 hrs. The leakage current density of the film is found to be 4x10^‐8 A/cm² from I‐V measurements.     

Influence of the temperature and the oxygen partial pressure on the phase formation in the system Cu – Fe – O

Copper iron oxides, Cu_1‐xFe_2+xO₄ (0 ≤ x ≤ 0.5), have been synthesized by thermal oxidation of copper ‐ iron mixtures. In this process, the phase formation and the phase stability were investigated as function of the temperature (800°C – 1200°C) and the oxygen partial pressure (1.013 x 10¹ – 1.013 x 10⁵ Pa). The phase formation starts with the reaction of the metallic components to simple oxides (Fe₃O₄, Fe₂O₃, CuO). From these simple oxides, the formation of complex oxides requires a minimum temperature of 800°C. The synthesis of single phase spinel compounds Cu²⁺_1‐2x Cu¹⁺_xFe_2+xO_4±δ is realized for 0.1 ≤ x ≤ 0.5, using specific temperature – p(O₂) – conditions for a given value of x. Remarkably, to achieve our goal, we found that the increase of x implies that of the reaction temperature and/or a decrease of the p(O₂) in the reaction gas stream. Besides, a single phase spinel CuFe₂O₄ does not exist in the temperature / p(O₂)‐field investigated. Using the results of XRD ‐ phase analysis, T ‐ p(O₂) – x – diagrams were constructed. These diagrams allow the prediction of phase compositions expected for different synthesis conditions. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spin‐Hamiltonian parameters and local lattice structure for Pd(I) center in γ‐irradiated bis(acetylacetonato)palladium(II)

This paper reports on a theoretical analysis of spin‐Hamiltonian parameters and local lattice structure for Pd(I) center in γ‐irradiated Pd(II)(acac)₂. Through the crystal‐ and ligand‐field theory, the microscopic spin‐Hamiltonian parameters and local molecular structure for Pd(I) center in the γ‐irradiated Pd(II)(acac)₂ system have been studied by using the high‐order perturbation formulas and Newman's superposition model. Based on these calculations, it was found that the distance of the metal‐ligand bonds in the square planar complex for Pd(I) center in the γ‐irradiated Pd(II)(acac)₂ system increases by 0.1Å. To understand the detailed physical and chemical properties of the [Pd(I)(acac)₂]^2– complex, the contributions of the spin‐orbit coupling of ligand to spin‐Hamiltonian parameters for Pd(I) ion are considered. The theoretical results are in reasonable agreement with the experimental values. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

X‐ray diffraction analysis of powder and thin film of (Gd1‐x Yx)2O3 prepared by sol‐gel process

The mixed oxide (Gd_1‐xY_x)₂O₃ (0.0 ≤ x ≤ 1.0) were synthesized, as powder and thin film, by a sol‐gel process. X‐ray diffraction data were collected and crystal structure and microstructure analysis were performed using Rietveld refinement method. All samples were found to have the same crystal system and formed solid solutions over the whole range of x. The cationic distribution, Gd³⁺ and Y³⁺, over the two non‐equivalent sites 8b and 24d of the space group Ia3 is found to be random for all values of (x). The lattice parameter is found to vary linearly with the composition (x). Replacing Gd³⁺ and Y³⁺ by each other introduces a systemic decrease in the x‐coordinate of cation position (24d) and slight changes in the oxygen coordinates. Crystallite size and microstrain analysis is performed along different crystallographic directions and anisotropic changes are found with the composition parameter (x). The average crystallite size ranges from 75 to 149 nm and the r.m.s strain from 0.027 to 0.068 x10^‐2. Textured Gd_1.841Y_0.159O₃ (400) buffer layers, with a high degree of alignment in both out‐plane and in‐plan, are successfully grown on cube textured Ni (001) tape substrates by sol–gel dip coating process. The resulting buffer layers are crack‐free, pinhole‐free, dense and smooth. YbBa₂Cu₃O_7‐x (YbBCO) thin film could be (00l) epitaxially grown on the obtained buffer layer using sol–gel dipping technique. (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Substitution effects on ferroelectric,leakage current and anti‐fatigue characteristic of Bi4‐xSbxTi3O12 thin films

Bi_4‐xSb_xTi₃O₁₂ (BSTO) (x = 0, 0.03, 0.04, 0.05, 0.06 and 0.07) thin films have been fabricated on Pt/Ti/SiO₂/Si substrates by sol‐gel method. The effects of various Sb³⁺ content on microstructure and ferroelectric properties of systems are investigated. XRD show that Bi_4‐xSb_xTi₃O₁₂ (x≠0) thin films prefer (117) orientation. The substitution Sb³⁺ for Bi³⁺ reduces the grain size of the film surface. Compared to the BTO (x = 0) film, Bi_4‐xSb_xTi₃O₁₂ films display exciting electric properties. Especially when x = 0.04, the film Bi_3.96Sb_0.04Ti₃O₁₂ has achieved the max 2Pr value of 87μC/cm². This film also has a better anti‐fatigue characteristic, which can be up to 10¹⁰ switching cycles without fatigue. The leakage current density improved with J = 8×10⁻⁸ A/cm².     

Anisotropic Optical and Transport Properties of Trans-(Ch)X

We have produced fully oriented highly crystal 1ine trans-(CH)_X films, which exhibit dramatic polarization effects for light polarized parallel or perpendicular to the oriented (CH)_X-chains. The polarization behavior in the vicinity of the bandgap and of the characteristic IR-modes, including those which are introduced as a result of doping with ASF5 is presented. DC-conductivity measurements allow to deduce the conductivity anisotropy of δ_‖/δ_⊥ ～ 100 for undoped and I₂-doped trans-(CH)_x at 300 K.     

Low-Temperature Electron Spin Resonance in (TMTSF)2PF6 in the High Pressure Metallic Phase

Abstract

The electron spin resonance of (TMTSF)₂PF₆ has been observed at low fields (H_o < 110 Oe) in the high pressure, metallic phase (p > 6.5 kbar) in the temperature range 1-4^?K. The anisotropy in the g value is similar to that observed at ambient pressure above the metal-insulator transition. The linewidth is very narrow and the spin susceptibility strongly decreases as the superconducting transition is approached from above. We interpret this as evidence for singlet-paired superconductivity. Superconductivity is observed at 1.1 K and the critical field has angular dependence in the be plane. These observations lead us to conclude that (TMTSF)₂PF₆ is a singlet paired superconductor.     

4,4′-Di(N)Hexoxybenzalazine: Crystal and Molecular Structure and Phase Characterization of the Liquid Crystalline Compound

Abstract

The crystal and molecular structure of the mesogenic title compound (HBA) is described. Lattice parameters are: space group P1, a = 9.003(2) Å, b = 8.850(2) Å, c = 8.510(2) Å, α = 79.63(1)°, β = 65.04(1)°, γ = 87.41(1)° (at T = 299 K). The molecules contain a centre of symmetry and the phenyl rings are coplanar. In order to obtain better structural data for a comparison with its methoxy derivative (MBA) a redetermination of this structure was carried out using a new data set. The melting enthalpy of HBA is 45(2) kJmol^?1 (127.8(5)°C) its clearing enthalpy is 1.5(4) kJmol^?1 (153.2(5) °C). The fluctuation wave-length 2π/q_‖ of 27(2) Å in the nematic state can be compared with the molecular length of 31.63 Å.     

Synthesis and X-ray crystal structure of an organometallic phosphonate [η6-1,2-C6H4(OCH3)(P(O)(OCH2CH3)2)]Cr(CO)3

The chiral, racemic, arene phosphonate complex, [t⁶-1,2-C₆H₄(OCH₃t)(P(O)(OCH²CH₃t)²)t] Cr(CO)₃ (1), was prepared via the reaction of 1,2-C₆H₄(OCH₃)(P(O)(OCH²CH₃)²) with Cr(CO)₆ in refluxing dioxane/THF. The title complex crystallized in P1 with the cell dimensions: a = 8.4893(4) Å, b = 11.0638(9) Å, c = 11.2135(8) Å, and = 62.151(8), = 105.154(5), = 112.426(6), giving a volume of 856.34(10) ų. The conformation of 1 is described as eclipsed (E) in which the methoxy substituent eclipses a carbonyl ligand of the tripod, and the phosphonate substituent is staggered.     

Crystal structures of the new diphosphates,K2NiP2O7 and K6Sr2Ni5(P2O7)5

Crystalline K₂NiP₂O₇ (I): monoclinic, P2₁,a=9.230(2),b=17.540(8),c=8.319(9)Å, =91.44(2)°,Z=8,d _calc=3.067 g cm^–3, MoK =0.71069Å,R/R _w=6.5/9.4%, is characterized by the existence of face sharing NiO₆ octahedra with Ni–Ni separation of 2.827 Å (Ni–O; 1.93(2)–2.17(2)Å). K⁺ is seen in sites of seven, six, and fivefold coordination (K–O, averages; 2.83(2), 2.81(2), and 2.77(2)Å, respectively) P₂O₇ ^4– groups are observed in semieclipsed conformation. K₆Sr₂Ni₅(P₂O₇)₅ (II) crystallizes in monoclinic space group P2₁/c;a=11.038(7),b=9.533(13),c=7.438(2)Å, =100.13(4)°,D _calc=3.309 g cm^–3,Z=2,R/R _w=6.4/8.1%. Nickel atoms are distributed on planes parallel to the crystallographic (100) plane at =0 and =0.5. On the planes, =0, Ni²⁺ ions form successive linked trimers of edge sharing NiO₆ octahedra (Ni–Ni, 3.018(1), 3.008(1)Å; Ni–O, av 2.07(2)Å). The intermediate planes (=0.5) contain isolated and six coordinate Ni²⁺ ions (Ni–O av. 2.09(2)Å). Seven-coordinate potassium ions (K–O, av. 2.74(2)Å) are located on intermediate planes at =0.25 and 0.75. P₂O₇ ^4– groups are found in eclipsed conformation. Strontium atoms are located between nickel and potassium planes and are surrounded by seven oxygen atoms (Sr–O, av. 2.586(2)Å).     

Influence of Host Lattice in Interstital Dopant Sites: EPR Studies on Cu (II) Doped Sarcosine Cadmium Bromide Single Crystals

EPR study of Cu(II) doped in sarcosine cadmium bromide single crystals are carried out at room temperature. The impurity ions occupy the interstitial position in this crystal lattice. Crystalline field around the Cu(II) ion in this low symmetry crystal is rhombic. The transitions arise from a single paramagnetic site with g_xx = 2.1082, g_yy = 2.0005, g_zz = 2.2071, and A_xx = ‐64 x 10^‐4 cm^‐1, A_yy = ‐23 x 10^‐4 cm^‐1, A_zz =‐185 x 10^‐4 cm^‐1. The ground state is an admixture of dx2‐y2 and dz2 states. The observed molecular orbital coefficient value a2 = 0.85 reveals a moderate covalency of the s bonding and b2 = 0.967 indicates the weak pi bonding. A strong interaction between Cu(II) and nitrogen ligands is found to exist.     

Calculations of homogeneous region in Ga1−xAlxAs and GaAs1−xPx ternary solid solutions

Ternary solid solutions of A^IIIB^V compounds are considered as pseudobinary A(x)^IIIB(x)^v compounds, where the behaviour of A(x)^III and B(x)^v pseudoatoms is quite similar to A^III and B^v atoms in a binary A^IIIB^v crystal. Weak dependence of point defect contribution into Gibb's energy of A^IIIB^v crystal on its defect nature, random character of ternary solid solutions of A^IIIB^v compounds allow to use already for binary compounds developed formalism in the determination of component thermodynamic potentials of solid solution. Basing on literature data for the equilibrium solidus of AlAs the approximation for the temperature dependence of thermodynamic potential of an AB quasimolecule in A^IIIB^v crystal is revised. This result together with the well-known parameters for the equilibrium liquidus in Ga–P, Ga–As, and Al–As systems were used for calculations of the nonstoichiometric factor at the boundary of a homogeneous region in Ga_1−xAl_xAs and GaAs_1−xP_x ternary solid solutions. The results are compared with the known literature data.     

Effect of Ba ions substitution on multiferroic properties of BiFeO3 perovskite

Dielectric, magnetic and ferroelectric properties of Bi_1‐xBa_xFeO₃(x = 0.1, 0.2 and 0.3) synthesized by solid state reaction method are reported. X‐ray diffraction pattern showed that Bi_1‐xBa_xFeO₃was single phase. Ba substitution has led to a decrease in grain size and hence an increase in the electrical resistivity. The variation of dielectric constant and loss has been studied over a frequency range of 1 kHz – 2 MHz at room temperature. Ba doping leads to effective suppression of the spiral spin structure of BiFeO₃, resulting in the appearance of net magnetization. Improved multiferroic properties of Bi_0.8Ba_0.2FeO₃ ceramic with remnant magnetization and polarization 0.093 emu/g and 0.808 µC/cm², respectively, were obtained. The evidence of ferromagnetism and ferroelectric hysteresis loops in Bi_1‐xBa_xFeO₃system at room temperature makes it a good candidate for potential applications. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)