Flux growth of ZnO crystals doped by transition metals

ZnO crystals doped with Cr, Mn, Fe and Co were grown by the flux method. The prepared crystals revealed no phase separation detectable by X-ray diffraction. Structure properties were characterized by Raman and photoluminescence spectroscopy. For ZnO:Co, Mn and Cr, no spontaneous ferromagnetic moment was observed up to T=2 K whereas for the ZnO:Fe crystals the m(H) curves suggest the existence of 5 nm superparamagnetic iron clusters. At low temperatures the m(H) curves can be interpreted as a superposition of major paramagnetic and minor antiferromagnetic contribution. The paramagnetic part corresponds to the presence of Co²⁺, Fe³⁺, Mn²⁺ ions and small Cr atom clusters.     

Optical absorption spectra of LiNbO3, Fe:LiNbO3, and Zn:Fe:LiNbO3 single crystals grown by Bridgman method

The optical absorption spectra of LiNbO₃ (LN), Fe:LiNbO₃ (Fe:LN), and Zn:Fe:LiNbO₃ (Zn:Fe:LN) single crystals grown by Bridgman method were measured and compared. The absorption characteristics of the samples and the effects of growth process conditions on the absorption spectra were investigated. The Fe, Zn and Li concentrations in the crystals were analyzed by inductively coupled plasma (ICP) spectrometry. The results indicated that the overall Fe ion and Fe²⁺ concentration in Fe:LN and Zn:Fe:LN crystals increased along the growing direction. The incorporation of ZnO in Fe:LN crystal induced increase of Fe²⁺ in the crystal. Among Fe‐doped and Zn:Fe‐codoped LN single crystals, 3 mol% ZnO doped Fe:LN had a biggest change of Fe²⁺ ion concentration from bottom to top part of crystal. The effects of technical conditions (atmosphere and thermal history) on Fe²⁺ ion concentration were discussed. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hole defects in the crystal structure of synthetic lipscombite (Fe 4.7 3+ Fe 2.3 2+ )[PO4]4O2.7(OH)1.3 and genetic crystal chemistry of minerals of the lipscombite-barbosalite series

The crystal structure of a synthetic analog of the mineral lipscombite (Fe _2.3 ²⁺ Fe _4.7 ³⁺ )[PO₄]₄O_2.7(OH)_1.3 obtained under hydrothermal conditions in the LiF-Fe₂O₃-(NH₄)₂HPO₄-H₂O system is resolved (R = 0.040) by X-ray diffraction analysis (Bruker Smart diffractometer with a highly sensitive CCD detector, MoK _α radiation): a = 14.776(3) Å, b = 14.959(3) Å, c = 7.394(1) Å, β = 119.188(4)°, sp. gr. C2/c, Z = 4, ρ_exp = 3.8 g/cm³, ρ_calcd = 3.9 g/cm³. Fe²⁺ and Fe³⁺ cations are statistically distributed in each of four crystallographically independent positions, while occupying the corresponding octahedra with probabilities of 60, 90, 100, and 91%. The ratio Fe²⁺/Fe³⁺ in the composition of the crystals was established by Mössbauer spectroscopy. Lipscombite is interpreted as a mineral of variable composition described by the formula (Fe _x ²⁺ Fe _n?x ³⁺ )[PO₄]₄O_y(OH)_4?y . The field of stability is determined as a function of the iron content and the ratio Fe²⁺/Fe³⁺. It is shown that at n = 6 iron cations are ordered in octahedra and barbosalite structure is formed. An interpretation of genetically and structurally related members of the lipscombite family within a unified polysomatic series is proposed.     

Comparative characterization of defects formed by di-and trivalent metal dopants in KDP crystals and the structural mechanism of influence of impurities on face morphology

The structure of KDP crystals doped with trivalent (Al³⁺, Fe³⁺, Mn³⁺, V³⁺, and La³⁺) and divalent (Ni²⁺, Co²⁺, Fe²⁺, Mn²⁺, Ca²⁺, Sr²⁺, and Ba²⁺) cations was simulated by minimizing the energy of atomic interactions. Three types of defects were revealed: isolated defect centers formed by M ³⁺ and Ni²⁺ ions, cluster chain centers formed by M ²⁺ ions with ionic radii exceeding 0.9 Å, and complex centers formed via the replacement of potassium ions by large Ba²⁺ dopants with the simultaneous replacement of some of the phosphorus atoms by silicon ones. The corresponding energies of defect formation are calculated. The surface morphology of the crystal faces is studied. The changes in morphology in the presence of M ³⁺ dopants are caused by their adsorption, whereas for M ²⁺ dopants, these changes are caused mainly by their incorporation into the crystal structure.     

The defect structure of ammonium sulphate single crystals

The defect structure of larger ammonium sulphate crystals, grown from aqueous solutions, has been studied by means of X-ray diffraction topography after Lang's method. Several types of dislocations were identified. Moreover it was found that no relationship exists between growth rate and dislocation density, which implies that crystal growth proceeds via two-dimensional nucleation. No difference was found in the defect structure of crystals grown from pure water solutions and from aqueous solutions with 10 – 20% glycerine as additive: In both cases neither growth bands nor sector boundaries were found. On the other hand, crystals grown in aqueous solutions contaminated with Mn²⁺ and Fe³⁺ revealed growth bands and for Fe³⁺ a mosaic-like structure.     

Ikranite: Composition and structure of a new mineral of the eudialyte group

The crystal structure of a new mineral, ikranite, of the eudialyte group discovered in the Lovozero massif (the Kola Peninsula) was established by X-ray diffraction analysis. The crystals belong to the trigonal system and have the unit-cell parameters a = 14.167(2) Å, c = 30.081(2) Å, V = 5228.5 Å 3, sp. gr. R3m. Ikranite is the first purely ring mineral of the eudialyte group (other minerals of this group contain ring platforms of either tetrahedral or mixed types). It is also the first representative of the eudialyte group where Fe³⁺ prevail over Fe²⁺ ions.     

The Fe<Superscript>2+</Superscript>/Fe<Superscript>3+</Superscript> ratio in natural and heat-treated iron-rich eudialytes

The structures of natural iron-rich eudialyte (specimen 3458 from the Khibiny massif, the Kola Peninsula) and two heat-treated samples of this mineral calcined at 700 and 800°C were determined by X-ray diffraction. The trigonal unit-cell parameters (sp. gr. R3m) are as follows: a = 14.2645(1) Å, c = 29.9635(5) Å; a = 14.1307(1) Å, c = 30.1229(3) Å; a = 14.1921(2) Å, c = 30.2417(5) Å, respectively. It was found that Fe³⁺ ions in the calcined eudialytes, as well as impurities in the starting specimen, occupy the square-pyramidal Fe³⁺(V) sites, whereas Fe²⁺ ions are in the planar-tetragonal Fe²⁺(IV) sites.     

The ESR spectra of Mn<Superscript>2+</Superscript> ions and the low-temperature NQR spectra of <Superscript>175</Superscript>Lu in LuNbO<Subscript>4</Subscript> crystals

The electron-spin resonance spectra of Mn²⁺ ions and nuclear-quadrupole resonance spectra of ¹⁷⁵Lu are investigated to find out the possibility of implementing the technique of dynamic alignment of nuclei using LuNbO₄ single crystals doped with Mn²⁺. An estimate for the electron-spin resonance frequency of Mn²⁺ ions is obtained, and the temperature dependences of the quadrupole coupling constant eQq and the anisotropy parameter that characterizes the asymmetry of the electric field gradient at ¹⁷⁵Lu nuclei are studied. It is demonstrated that LuNbO₄ single crystals doped with Mn²⁺ ions can be used as working media in experiments on dynamic alignment of nuclei.     

Optical and magnetic properties of first-row transition metal ions in lead-silicate glass

First-row transition metal ions in lead-silicate glasses of composition: 37.9% mol PbO, 61.8% mol SiO₂ have been studied with regard to the oxidation state and the coordination by means of optical and magnetic measurements. Optical spectra have been recorded at 300 and 77 K. All the observed bands are assigned as being due to d-d transitions in T_d and/or O_h fields. Magnetic moments are of the order of the spin-only values. By ESR measurements we reveal and quantify titanium, vanadium and manganese oxidation states not detectable by the other techniques.It turns out that the various metal ions have the following oxidation states: Ti³⁺ and Ti⁴⁺, V⁴⁺ and V⁵⁺, Cr³⁺ and Cr⁶⁺, Mn²⁺ and Mn³⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺. The coordination is 4-fold for Ti⁴⁺ and V⁵⁺ and 6-fold for Mn³⁺ and Cu²⁺. Moreover it has been found that Fe³⁺, Co²⁺ and Ni²⁺ are both 4-fold and 6-fold coordinated and that Cr³⁺ and Cr⁶⁺ oxidation states coexist in the same sample.     

Synthesis and crystal chemical characteristics of the structure of <Emphasis Type="Italic">M</Emphasis><Subscript>0.5</Subscript>Zr<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> phosphates

Double phosphates of zirconium and metals with an oxidation degree of +2 of the composition M_0.5Zr₂(PO₄)₃ (M = Mg, Ca, Mn, Co, Ni, Cu, Zn, Sr, Cd, and Ba) are synthesized and characterized by X-ray diffraction methods and IR spectroscopy. The crystal structures of all the compounds are based on three-dimensional frameworks of corner-sharing PO₄-tetrahedra and ZrO₆-octahedra. Phosphates with large Cd²⁺, Ca²⁺, Sr²⁺, and Ba²⁺ cations octahedrally coordinated with oxygen atoms form rhombohedral structures (space group R3), whereas phosphates with small tetrahedrally coordinated Mg²⁺, Ni²⁺, Cu²⁺, Co²⁺, Zn ²⁺, and Mn²⁺-cations are monoclinic (space group P2₁/n). The effect of various structure-forming factors on the M_0.5Zr₂(PO₄)₃ compounds with a common structural motif but different symmetries are discussed.     

Cation distribution in the structure of titanium-containing ludwigite

The crystal structure of natural titanium-containing ludwigite has been refined. The unit-cell parameters are a = 9.260 ± 0.002 Å, b = 12.294± 0.002 Å, c = 3.0236± 0.0005 Å, sp. gr. Pbam, and R = 0.0288. The observed cation distribution over the M1-M4 positions corresponds to the structural formula (Mg_0.5)(Mg_1.0)(Mg_0.338Fe _0.162 ²⁺ )(Fe _0.47 ³⁺ Ti _0.21 ⁴⁺ Mg _0.15 ²⁺ Al _0.10 ³⁺ Fe _0.07 ²⁺ (BO₃)O₂. Highly charged titanium ions in the M4 position are balanced mainly with magnesium and not with divalent iron ions.     

Pyroxenoids of pyroxmangite–pyroxferroite series from xenoliths of Bellerberg paleovolcano (Eifel,Germany): Chemical variations and specific features of cation distribution

The pyroxferroite and pyroxmangite from xenoliths of aluminous gneisses in the alkaline basalts of Bellerberg paleovulcano (Eifel, Germany) have been studied by electron-probe and X-ray diffraction methods and IR spectroscopy. The parameters of the triclinic unit cells are found to be a = 6.662(1) Å, b = 7.525(1) Å, c = 15.895(2) Å, α = 91.548(3)°, β = 96.258(3)°, and γ = 94.498(3)° for pyroxferroite and a = 6.661(3) Å, b = 7.513(3) Å, c = 15.877(7) Å, α = 91.870(7)°, β = 96.369(7)°, and γ = 94.724(7)° for pyroxmangite; sp. gr. \(P\overline 1 \). The crystallochemical formulas (Z = 2) are, respectively, ^M(1–2)(Mn_0.5Ca_0.4Na_0.1)₂^M(3–6)(Fe, Mn)₄^M7[Mg_0.6(Fe, Mn)_0.4][Si₇O₂₁] and ^M(1–3)(Mn, Fe)₃^M(4–6)[(Fe, Mn)_0.7Mg_0.3]₃^M7[Mg_0.5(Fe, Mn)_0.5][Si₇O₂₁]. For these and previously studied representatives of the pyroxmangite structural type, an analysis of the cation distribution over sites indicates wide isomorphism of Mn²⁺, Fe²⁺, and Mg in all cation M(1–7) sites and the preferred incorporation of Сa and Na into large seven-vertex M1O₇ and M2O₇ polyhedra and Mg into the smallest five-vertex M7O₅ polyhedron.     

A Crystallizer for Growing Large Singe Crystals from Solution under Steady-State Concentration Convection Conditions

A crystallizer for growing large single crystals from solution under steady-state concentration convection conditions is described. The crystallizer has only one vessel divided by a drilled plate in two compartments kept at different temperatures. The convection of concentration occurs through the dividing plate between the compartments. The crystallizer was used for growing KDP and TGS single crystals. Mass- and heat transfer equations are derived. Growth rate calculations may be carried out using the derived equations. Growth rate measurements of KDP crystals have been performed. The overall heat transfer coefficient for the transfer of heat through the dividing plate is also experimentally determined. Light absorption, ESR and Mössbauer spectra have shown the presence of Fe⁺², Cr⁺³ and Mn⁺² ions in the (100) greenish zones of KDP crystals.     

Specific features of the substitution of Fe<Superscript>3+</Superscript> impurity ions for Zr<Superscript>4+</Superscript> in NaZr<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> single crystals

The EPR spectra of Fe³⁺ impurity ions in NaZr₂(PO₄)₃ single crystals at 300 K are investigated, and the spin Hamiltonian of these ions is determined. A comparative analysis of the spin-Hamiltonian and crystal-field tensors is performed using the maximum invariant component method. It is demonstrated that Fe³⁺ impurity ions substitute for Zr⁴⁺ ions with local compensator ions located in cavities of the B type. It is revealed that the invariant of the spin-Hamiltonian tensor B₄ and the crystal-field tensor V ₄ ⁴⁴ depend substantially on the mutual arrangement of ions in the first and second coordination spheres. The corresponding dependences are analyzed.     

Crystal structure of magnesioferrikatophorite

The crystal structure of the Na,Ca-amphibole magnesioferrikatophorite found in carbonatites from the Turiy Cape (Kola Peninsula) was refined (Siemens P4 diffractometer, λMoK _α radiation, 1481 independent reflections with |F|>4σ(F), anisotropic refinement, R(F) = 0.039). The parameters of the monoclinic unit cell are a = 9.875(5) Å, b = 18.010(8) Å, c = 5.309(3) Å, β = 104.39(5)°, sp. gr. C2/m, Z = 2. The distribution of the cations over the crystallographically nonequivalent M(1–4)-positions was revealed by Mössbauer spectroscopy and X-ray diffraction analysis. The character of splitting of the A-position correlates with the characteristic features of the magnesioferrikatophorite composition. The resulting structural formula (Na_0.87K_0.13)_{Σ = 1} · (Na_1.18Ca_0.82)_{Σ = 2}(Mg_1.41Fe _0.42 ³⁺ Ti _0.17 ⁴⁺ )_{Σ= 2} Fe _1.31 ³⁺ Mg_0.69)_{Σ = 2}(Mg_0.60Fe _0.38 ²⁺ Mn_0.02)_{Σ = 1}(Si_3.16Al_0.84)_{Σ = 4} · Si₄O₂₂(O_1.05OH_0.66F_0.29)_{Σ= 2} agrees well with the electron microprobe analysis data. Based on the zonal character of the crystal and high Fe ³⁺ content, the conditions of crystallogenesis are defined as oxidative against the background of a decrease in the Na potential in the course of the evolution of a mineral-forming system.     

Growth and characterization of Mn2+ doped calcium l‐tartrate crystals

Single crystals of Mn²⁺ doped calcium levo‐ tartrate tetrahydrate (CLTT) were grown by single diffusion gel growth technique in silica hydro‐gel media. The doping of Mn²⁺ was varied by mixing 0.001M, 0.005M, 0.01M, 0.05M, and 0.1M solutions of MnCl₂ with 1M CaCl₂ solution in equal volumes in the supernatant solutions. The actual amount of Mn²⁺ doping in CLTT crystals was estimated by ICP (Inductively Coupled Plasma) technique. The powder XRD of the samples suggested no significant change in the unit cell dimensions and the presence of any extra phase. The FT‐IR spectra indicated the presence of water molecule, O‐H bond, C‐O bond and carbonyl C=O bond. The EPR spectra confirmed the presence of Mn²⁺ ions in the crystals. The variation of the dielectric constant with temperature confirmed the earlier results of pure calcium tartrate crystals and indicated the ferroelectric nature of the doped crystals. As the amount of doping of Mn²⁺ increased the value of dielectric constant increased. The results are discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal structure of the NaCa(Fe<Superscript>2+</Superscript>, Al,Mn)<Subscript>5</Subscript>[Si<Subscript>8</Subscript>O<Subscript>19</Subscript>(OH)](OH)<Subscript>7</Subscript> · 5H<Subscript>2</Subscript>O mineral: A new representative of the palygorskite group

A specimen of a new representative of the palygorskite-sepiolite family from Aris phonolite (Namibia) is studied by single-crystal X-ray diffraction. The parameters of the triclinic (pseudomonoclinic) unit cell are as follows: a = 5.2527(2) Å, b = 17.901(1) Å, c = 13.727(1) Å, α = 90.018(3)°, β = 97.278(4)°, and γ = 89.952(3)°. The structure is solved by the direct methods in space group P \(\bar 1\) and refined to R = 5.5% for 4168 |F| > 7σ(F) with consideration for twinning by the plane perpendicular to y (the ratio of the twin components is 0.52: 0.48). The crystal chemical formula (Z = 1) is (Na_1.6K_0.2Ca_0.2)[Ca₂(Fe _3.6 ²⁺ Al_1.6Mn_0.8)(OH)₉(H₂O)₂][(Fe _3.9 ²⁺ Ti_0.1)(OH)₅(H₂O)₂][Si₁₆O₃₈(OH)₂] · 6H₂O, where the compositions of two ribbons of octahedra and a layer of Si tetrahedra are enclosed in brackets. A number of specific chemical, symmetrical, and structural features distinguish this mineral from other minerals of this family, in particular, from tuperssuatsiaite and kalifersite, which are iron-containing representatives with close unit cell parameters.     

Synthesis and crystal structure of new phosphate NaFe 4 2+ Fe 3 3+ [PO4]6

New sodium iron orthophosphate NaFe ₄ ²⁺ Fe ₃ ³⁺ [PO₄]₆ was synthesized by the hydrothermal method. The crystal structure (sp. gr. $P\bar 1$ ) was established by the heavy-atom method, with the exact chemical formula of the compound being unknown; R _hkl = 0.0492, R _whkl = 0.0544, S = 0.52. The new compound is analogous to iron phosphate Fe ₃ ²⁺ Fe ₄ ³⁺ [PO₄]₆ studied earlier. However, these two compounds differ in the Fe²⁺ and Fe³⁺ contents, because Na⁺ ions in the new compound are located at the centers of symmetry not occupied earlier.     

Irradiation-induced change of valence of Cr3+ ions doped in alkali sulphates

It is shown by means of investigation of both optical absorption spectra and Roentgen K-lines of chromium doped in LiKSO₄, LiNaSO₄, and Li₂SO₄ · H₂O crystals, that X-irradiation results in change of the impurity charge in a following way: Cr³⁺ + h → Cr⁴, Cr⁴⁺ + h → Cr⁵⁺.     

Change in the crystal structure of zink(II) sulphate heptahydrate and magnesium(II) sulphate heptahydrate due to isodimorphous substitution by copper(II), iron(II), and cobalt(II) ions

The physico-chemical analytical data on the systems ZnSO₄(MgSO₄)–CuSO₄(FeSO₄, CoSO₄ resp.)–H₂O at 25.0°C have shown that due to isodimorphous substitution of Zn²⁺, Mg²⁺ resp., in the orthorhombic crystals of ZnSO₄ · 7 H₂O MgSO₄ · 7 H₂O, resp. for Cu²⁺, Fe²⁺ or Co²⁺ above a specific degree of ionic substitution, the orthorhombic crystals are converted into monoclinic mixed crystals. The crystal phases are characterized by X-ray diffraction, microscopic and optical studies. The dominant effect of the admixed Cu²⁺, Fe²⁺, Co²⁺ ions is explained in terms of their electronic configurations, for which, owing to the operation of the Jahn-Teller effect, a deformation of the regular octahedral arrangement of the water ligands about the metal ion is found to occur. The strongest deforming effect is that of Cu²⁺ ions followed by the Fe²⁺ ions, the weakest deforming effect being that of Co²⁺ ions.