Structural defects in PbMoO4 single crystals doped with Co ions

Pure and Co-doped PbMoO₄ crystals, were studied using reflection high energy electron diffraction (RHEED), optical and dielectric methods. The calculated lattice constants for PbMoO₄:Co (0.2 mol%) were determined as being equal to: a = 5.54 ± 0.05 Å and c = 11.96 ± 0.05 Å. The absorption spectra of “as grown” and annealed pure and Co-doped PbMoO₄ crystals were examined. The results of dielectric measurements gave the conductivity activation energy of highly Co-doped PbMoO₄ crystals (0.5 and 1.0 mol%) equal to 0.40 and 0.46 eV, respectively.     

Electron paramagnetic resonance (EPR) investigations of the local environment around Co2+ ions doped in PbMoO4 single crystals – Correlation with optical studies

The electron paramagnetic resonance (EPR) measurements of PbMoO₄ single crystals doped with Co²⁺ ions (0.5 wt.%) carried out at temperature range 10–12 K are reported. The observed spectra reveal evidently two major groups of EPR spectra, each group consists of eight hyperfine structure components associated with the Co nuclear spin I = 7/2. Additionally, EPR spectra of the unintentional impurities have been observed, which have been assigned to Nd³⁺ ions in PbMoO₄. The analysis of the various characteristic features of the EPR spectra as well as our earlier optical absorption studies of Co²⁺:PbMoO₄ indicate that the Co²⁺ ions are located at two crystallographically distinct complexes, denoted Co²⁺(α) and Co²⁺(β). The fictitious ‘spin’ S′ = ½ has been assigned to the observed ground Kramers doublet state of each of the two Co²⁺ complexes tentatively identified as located at the Mo sites in PbMoO₄. The spin Hamiltonian parameters for Co²⁺ (S′ = ½) ions in PbMoO₄, including the components of the Zeeman and hyperfine structure tensors g_ij and A_ij, respectively, are experimentally determined for the first time. Comparison of our results with the values of g_ij and A_ij for Co²⁺ ions in other structurally similar compounds further strengthens this conclusion. Correlation of the present results with those obtained earlier from optical studies is discussed. Alternative assignments of the ground states and options for the origin of the ‘spin’ S′ = ½ for Co²⁺ ions in PbMoO₄ will be considered in a subsequent paper.     

Hydrothermal synthesis,crystal structure and characterization of LiCoP5O14·H2O: A new condensed layered penta phosphate crystals

A new family of condensed hydrated lithium cobalt penta phosphate (LiCoP₅O₁₄·H₂O) crystals were synthesized by hydrothermal technique and characterized by X-ray diffraction method. The compound crystallizes in monoclinic system with space group P21/c and cell parameters a = 10.788(4) Å, b = 9.761(3) Å, c = 9.788(5) Å, β = 101.249(1) Å, Z = 4, exhibiting layer type polymeric structure. DTA study indicates that this compound has low thermal stability and magnetically frequency dependent paramagnetic behaviour.     

Preparation,characterization and dielectric properties of Ba5LnZnTa9O30 (Ln=La,Sm) ceramics

Ba₅LnZnTa₉O₃₀ (Ln=La, Sm) ceramics were prepared by high temperature solid-state reaction route. The samples were characterized by X-ray diffraction, scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) methods. They belong to paraelectric phase of filled tetragonal TB structure at room temperature with unit cell a=12.5909(4) Å, c=3.9622(2) Å for Ba₅LaZnTa₉O₃₀; and a=12.5777(4) Å, c=3.9544(2) Å for Ba₅SmZnTa₉O₃₀. At 1 MHz, Ba₅LaZnTa₉O₃₀ has high dielectric constants of 89 with low dielectric loss 0.0067, and temperature coefficients of the dielectric constant (τ_ε) −811 ppm °C⁻¹; Ba₅LaZnTa₉O₃₀ has dielectric constants of 74 with low dielectric loss 0.0035, and τ_ε −474 ppm °C⁻¹.     

Ba2La2TiNb2O12: A new microwave dielectric of A4B3O12-type cation-deficient perovskites

A new A₄B₃O₁₂-type cation-deficient perovskite Ba₂La₂TiNb₂O₁₂ was prepared by the conventional solid-state reaction route. The phase and structure of the ceramics were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). The compound crystallizes in the trigonal system with unit cell parameter a = 5.6726(3) Å, c = 27.740(2) Å, V = 773.04(9) ų and Z = 3. The microwave dielectric properties of the ceramic were studied using a network analyzer, and it shows a high dielectric constant of 42.70, a high quality factor with Q × f of 31,130 GHz, and a small negative τ_f of − 4.2 ppm °C^− 1.     

Preparation,phase structure and microwave dielectric properties of CoLi2/3Ti4/3O4 ceramic

A new low loss microwave dielectric ceramic with composition of CoLi_2/3Ti_4/3O₄ was prepared by a conventional solid-state reaction method. The compound has a cubic spinel structure [Fd-3m (227)] similar to MgFe₂O₄ with lattice parameters of a = 8.3939 Å, V = 591.42 Å³, Z = 8 and ρ = 4.30 g/cm³. This ceramic has a low sintering temperature (～1050 °C) and good microwave dielectric properties with relative permittivity of 21.4, Q × f value of 35,000 GHz and τ_f value of ?22 ppm/°C. Furthermore, the addition of BaCu(B₂O₅) (BCB) can effectively lower the sintering temperature from 1050 °C to 900 °C and does not induce much degradation of the microwave dielectric properties. Compatibility with Ag electrode indicates that the BCB added CoLi_2/3Ti_4/3O₄ ceramics are good candidates for LTCC applications.     

X-ray powder diffraction,vibration and thermal studies of [A0.92(NH4)0.08]2TeCl4Br2 with A = Cs,Rb: Influence of mixed cationic and anionic substitutions

The crystal structures of [A_0.92(NH₄)_0.08]₂TeCl₄Br₂ with A = Cs, Rb have been determined using X-ray powder diffraction techniques. The two compounds crystallize in the tetragonal space group P4/mnc, with the unit cell parameters: a = 7.452(1) Å, c = 10.544(3) Å, Z = 2 and a = 7.315(2) Å, c = 10.354(4) Å, Z = 2 in the presence of Cs and Rb, respectively. These two compounds have an antifluorite-type arrangement of NH₄⁺/Rb⁺/Cs⁺ and octahedral TeCl₄Br₂^2? anions. The stability of these structure is by ionic and hydrogen bonding contacts: A?Cl, A?Br and N–H?Cl, N–H?Br. The different vibrational modes of these powders were analysed by FTIR and Raman spectroscopic studies. A DTA/TGA experiment reveals one endothermic peak at 780 K implicating the decomposition of the sample. At low temperature, one endothermic peak in thermal behavior is detected at around 213 K by DSC experiment. This transition was confirmed by dielectric measurements.     

Synthesis,structure, growth and characterization of a novel organic NLO single crystal: Morpholin-4-ium p-aminobenzoate

The title compound, morpholin-4-ium p-aminobenzoate (MPABA)(C₄H₁₀NO⁺,C₇H₆NO₂^?), has been synthesized for the first time by the addition of morpholine with 4-aminobenzoic acid in equi-molar ratio and good quality single crystals have been grown by solution growth technique using methanol as a solvent. The molecular structure of the compound was solved and refined by Direct Methods using SHELXS97 and full-matrix least-squares technique using SHELXL97, respectively. MPABA crystallizes in a monoclinic system with unit cell parameters, a = 5.948(5) Å, b = 18.033(4) Å, c = 10.577(5) Å, β = 90.40(1)° and non-centrosymmetric space group Cc. The experimentally measured density and chemical compositions were found to be in good agreement with the theoretical values. The phases and functional groups of MPABA have been identified and confirmed through powder X-ray diffraction and Fourier transform infrared (FTIR) studies, respectively. The thermal stability and decomposition details were studied through TG/DTA thermograms. The UV–visible transmission spectra were recorded for the grown crystal and its NLO characteristic was explored by powder second harmonic generation (SHG) studies.     

Nd2Ba2CaCu2−xZnxTi3O14: a new family of tunable dielectric oxides showing a compositionally controlled tetragonal to cubic transition

Oxides of the formula Nd₂Ba₂CaCu_2−xZn_xTi₃O₁₄ (x=0.0, 0.5, 1.0, 1.5, 2.0) have been successfully prepared by high temperature ceramic route at 1025 °C, as well as by the low temperature citrate precursor route at 800 °C. The copper-rich compounds obtained by the ceramic route (x=0–1.0) are found to have a tetragonal structure, with the a and c parameters increasing with zinc substitution, from a=3.913(8) Å and c=19.63(1) Å for x=0, to a=3.925(1) Å and c=19.64(1) Å for x=1. The tetragonal distortion decreases with increase in zinc substitution and the oxides with x>1.5 were found to crystallize in the cubic structure with a=3.933(2) and a=3.937(1) Å for the x=1.5 and two compositions, respectively. The entire range of oxides (0≤x≤2) could be obtained as pure phases at 800 °C and crystallize in the cubic structure when prepared by the citrate precursor route. The room temperature dielectric constant (ε) at 100 kHz varies from 8 for the pure Cu composition and increased to 59 for the pure Zn analog. The dielectric constant depends on the synthetic route—the pure Zn compound Nd₂Ba₂CaZn₂Ti₃O₁₄ gave much lower dielectric constant (ε) of 23 at 100 kHz when prepared by the citrate precursor method (ε=59, solid state route).     

Synthesis and structure determination of new open-framework chromium carboxylate MIL-105 or CrIII(OH)·{O2C–C6(CH3)4–CO2}·nH2O

Two new three-dimensional chromium(III) dicarboxylate, MIL-105 or Cr^III(OH)·{O₂C-C₆(CH₃)₄-CO₂}·nH₂O, have been obtained under hydrothermal conditions, and their structures solved using X-ray powder diffraction data. Both solids are structural analogs of the known Cr benzenedicarboxylate compound (MIL-53). Both contain trans corner-sharing CrO₄(OH)₂ octahedral chains connected by tetramethylterephthalate di-anions. Each chain is linked by the ligands to four other chains to form a three-dimensional framework with an array of 1D pores channels. The pores of the high temperature form of the solid, MIL-105ht, are empty. However, MIL-105ht re-hydrates at room temperature to finally give MIL-105lt with pores channels filled with free water molecules (lt: low temperature form; ht: high temperature form). The thermal behaviour of the two solids has been investigated using TGA. Crystal data for MIL-105ht: monoclinic space group C2/c with a = 19.653(1) Å, b = 9.984(1) Å, c = 6.970(1) Å, β = 110.67(1)° and Z = 4. Crystal data for MIL-105lt: orthorhombic space group Pnam with a = 17.892(1) Å, b = 11.165(1) Å, c = 6.916(1) Å and Z = 4.     

Synthesis and characterization of a one-dimensional inorganic–organic hybrid iron phosphate: [Fe(bipy)(HPO4)(H2PO4)] (bipy = 2,2′-bipyridyl) with anti-ferromagnetic property

A coordinated iron phosphate, Fe(bipy)(HPO₄)(H₂PO₄) (I), has been hydrothermally synthesized and characterized by elemental analysis, thermogravimetric analysis, and single crystal X-ray diffraction. The title compound crystallizes in the monoclinic system, space group P2₁/n (No. 14), with cell parameters M = 405.00, a = 10.904(4) Å, b = 6.4210(2) Å, c = 19.294(9) Å, β = 101.24(4) ų, V = 1324.9(9) ų, Z = 4, R₁ [I > 2((I)) = 0.0357, wR₂ [I > 2((I)) = 0.0717. This compound displays a new structure of ladder-like chains, in which each one-dimensional chain is constituted by the distorted octahedral units of Fe³⁺ bridged through PO₄ tetrahedra. The bipy ligands in the compound bind in a bidentate fashion to the iron atoms and the ladder-like structure of the compound extends into a three-dimensional supramolecular array via π–π stacking interactions of bipy ligands and strong hydrogen bonding between the chains. Mössbauer spectroscopy shows the presence of Fe³⁺ in the octahedral coordination. Magnetic susceptibility measurements show that this material may model as anti-ferromagnetic.     

Synthesis,characterization and electrochemical studies on LiCoAsO4

LiCoAsO₄ is synthesized by solid state reaction method and its crystal structure has been refined by the Rietveld method using powder X-ray diffraction data. LiCoAsO₄ crystallizes in olivine structure with space group Pnma and orthorhombic lattice parameters are a = 10.4614(2) Å, b = 5.9970(1) Å and c = 4.8866(1) Å. Electrochemical studies reveal that in LiCoAsO₄, lithium is deintercalated and intercalated at high voltage ∼5.0 V. On the other hand, the compound can react with about 9Li on discharge to 0.05 V. A reversible capacity of ∼100 mAh/g is obtained in the voltage range 1.0–2.5 V.     

Fluorine intercalation in the n = 1 and n = 2 layered manganites Sr2MnO3.5+x and Sr3Mn2O6

Fluorine insertion into the oxygen defect superstructure manganite Sr₂MnO_3.5+x has been shown by transmission electron microscopy (TEM) to result in two levels of fluorination. In the higher fluorine content sections, the fluorine anions displace oxygen anions from their apical positions into the equatorial vacancies, thus destroying the superstructure and reverting to a K₂NiF₄-type structure (a = 3.8210(1) Å and c = 12.686(1) Å). Conversely, lower fluorine content sections retain the Sr₂MnO_3.5+x defect superstructure, crystallising in the P2₁/c space group. Fluorine intercalation into the reduced double-layer manganite Sr₃Mn₂O₆ occurs in a step-wise fashion according to the general formula Sr₃Mn₂O₆F_y with y = 1, 2, and 3. It is proposed that the y = 1 phase (a = 3.815(1) Å, c = 20.29(2) Å) is produced by the filling of all the equatorial oxygen vacancies by fluorine atoms whilst the y = 2 phase (a = 3.8222(2) Å, c = 21.2435(3) Å) has a random distribution of fluorine anions throughout both interstitial rocksalt and equatorial sites. Neutron powder diffraction data suggest that the fully fluorinated y = 3 phase (a = 3.8157(6) Å, c = 23.666(4) Å) corresponds to the complete occupation of all the equatorial oxygen vacancies and the interstitial sites by intercalated fluorine.     

Synthesis,characterization and crystal structure of a novel Strandberg-type polyoxoselenomolybdate Rb4[Se2Mo5O21]·2H2O

An inorganic compound formulated as Rb₄[Se₂Mo₅O₂₁]·2H₂O (1) has been isolated by conventional solution method and structurally characterized by single-crystal X-ray diffraction methods, scanning electron microscopy (SEM), powder XRD, IR, UV–vis spectra, and cyclic voltammetry measurements. This compound crystallizes in the monoclinic system, space group C2 with unit a = 19.701 (3) Å, b = 10.296 (2) Å, c = 12.134 (4) Å, β = 106.96 (2)° and Z = 4. The crystal structure of (1) is built up from a Strandberg clusters connected through hydrogen-bonding interactions into a three-dimensional supramolecular network.     

Variation of electro-optic coefficients in MgO-doped LiNbO3 single crystals

Maker fringe experiment was performed to investigate a variation of second-harmonic generation by external DC field as a function of MgO content in MgO-doped LiNbO₃ crystals. The 4 mol% MgO-doped LiNbO₃ has the largest value of the electro-optic coefficient (Γ) among all MgO-doped LiNbO₃ crystals, which is 1.05 × 10^− 5 cm/kV. The threshold phenomena was revealed in between 4 mol% MgO-doped LiNbO₃ and 5 mol% MgO-doped one.     

Mechanochemical synthesis of a La0.67Ce0.21Nd0.08Pr0.04Ni5 intermetallic compound

The mechanochemical synthesis of a La_0.67Ce_0.21Nd_0.08Pr_0.04Ni₅ intermetallic is studied. The intermetallic is synthesised from a mixture of LaNi₅ and La_0.25Ce_0.52Nd_0.17Pr_0.06Ni₅. The processes controlling the mechanical alloying are characterised as a function of integrated milling time (t_m). Effects of fracture and cold welding on the sample are identified by scanning electron microscopy. Compositional, microstructural and structural changes are analysed by energy dispersive spectroscopy and X-ray diffraction. The powder obtained has a particle size distribution of 9 ± 1 μm with an average crystallite size of 370 ± 10 Å and strain >10%. The intermetallic compound is annealed in Ar to increase crystallite size and to release strain. The structure is refined by the Rietveld method. Cell parameters are a = 4.982(2) Å and c = 3.980(9) Å, respectively. The advantage of the synthesis method using intermetallics instead of metals/alloys is discussed along with the characteristics of the powder obtained.     

Preparation,crystal structure and characterization of α-NaSbP2S6 and β-NaSbP2S6 phases

The new phases α-NaSbP₂S₆ and β-NaSbP₂S₆ were synthesized by ceramic and reactive flux methods at 773 K. The structures of α-NaSbP₂S₆ and β-NaSbP₂S₆ were determined by the single-crystal X-ray diffraction technique. α-NaSbP₂S₆ crystallizes in the monoclinic space group P2₁/c with a = 11.231(2) Å, b = 7.2807(15) Å, c = 11.640(2) Å, β = 108.99(3)°, V = 900.0(3) Å³ and z = 4. β-NaSbP₂S₆ crystallizes in the monoclinic space group P2₁ with a = 6.6167(13) Å, b = 7.3993(15) Å, c = 9.895(2) Å, β = 92.12(3) °, V = 484.10(17) Å³ and z = 2.The α- and β-phases of NaSbP₂S₆ are closely related, the main difference lies in the stacking of the [Sb[P₂S₆]]_nⁿ⁻ layers. The structure of α-NaSbP₂S₆ consists of two condensed layers (MPS₃ type) to give an ABAB… sequence with Na⁺ cations located in the interlayer space. The packing of β-NaSbP₂S₆ is formed by monolayers of [Sb[P₂S₆]]_nⁿ⁻ stacked in an AA… fashion separated by a layer of Na⁺ cations. Both phases are derivates of the M¹⁺M³⁺P₂Q₆ family.The optical band gaps of α-NaSbP₂S₆ and β-NaSbP₂S₆ were determined by UV–vis diffuse reflectance measurements to be 2.17 and 2.25 eV, respectively.     

Influence of copper substitution on magnetic and electrical properties of MgCuZn ferrite prepared by microwave sintering method

Polycrystalline MgCuZn ferrites with chemical formula Mg_0.50-xCu_xZn_0.50Fe₂O₄ (x = 0.00, 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30) were prepared by microwave sintering method. These powders were calcined, compacted and sintered at 950 °C for 30 min. Structural, microstructural and elemental analyses were carried out using X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectrometry (EDS), respectively. The lattice parameter is found to increase with increasing copper content. A remarkable densification is observed with the addition of Cu ions in the ferrites. The sintered ferrite was characterized for initial permeability, dielectric constant and dielectric loss tangent and ac conductivity measurements. The temperature variation of the initial permeability of these samples was carried out from 30 °C to 200 °C. The dielectric constant, dielectric loss tangent and ac conductivity have been measured in the frequency range of 100 Hz to 1 MHz. Initial permeability and dielectric constant were found to increase and dielectric loss decreased with Cu substitution for Mg, up to x = 0.20. The ferrite powder prepared is suitable for the application in multilayer chip inductor due to its low-temperature sinterability, good magnetic properties and low loss at high frequency.     

Synthesis and characterization of a new organic sulphate, [2,3-(CH3)2C6H3NH3]HSO4·H2O

Crystals of a new hybrid compound C₈H₁₂N⁺, HSO₄^?·H₂O were synthesized in aqueous solution and characterized by X-ray diffraction and IR absorption spectroscopy. This compound crystallizes in the orthorhombic non-centrosymmetrical space group P2₁2₁2₁ and an unit cell with a = 5.74(2) Å, b = 9.17(2) Å, c = 21.34(4) Å, V = 1124(6) Å³, and Z = 4. Its crystal structure is a packing of alternated inorganic and organic layers parallel to (a,b) planes. The different components are connected by a bi-dimensional network of strong OH…O and NH…O hydrogen bonds. Then, in order to detect phase transitions and watch changes in the conductivity behaviour, investigations by DTA–TG and differential scanning calorimetry (DSC) and electrical conductivity measurements were carried out.     

Synthesis,crystal structure and properties of a new lead fluoride borate,Pb3OBO3F

A new compound, Pb₃OBO₃F, has been grown by the high temperature solution method from the PbO–PbF₂–B₂O₃ system. It crystallizes in the orthorhombic system, space group Pbcm with unit-cell parameters a = 7.6313(14) Å, b = 6.5229(12) Å, c = 11.906(2) Å, Z = 4, volume = 592.66(19) Å³. The structure of the compound is solved by the direct methods and refined to R₁ = 0.0528 and wR₂ = 0.1400. Pb₃OBO₃F consists of Pb(1)O₃F tetrahedra, Pb(2)O₄ tetrahedra and BO₃ triangles which build up the symmetrical chains extended along the c-axis. The powder X-ray diffraction pattern of the Pb₃OBO₃F has been measured. Functional groups presented in the sample were identified by Fourier transform infrared spectrum.