Thermal induced structural properties of silver(I) sulphate (Ag2SO4)

The crystal structures of silver(I) sulphate, Ag₂SO₄, have been investigated as a function of temperature. A main feature is the phase transition from the low‐temperature ordered phase, F ddd, to the high‐temperature disordered phase, . In particular, the high‐temperature structure is solved from single crystal synchrotron X‐ray measurements. In this phase the title compound undergoes a colossal (anisotropic) thermal expansion of . This is presumably owing to a high anisotropic vibration state of one of the two crystallographically independent Ag‐atoms. Simultaneously occurring high ionic conductivity may be associated with silver ions moving along the ‐axis using a “paddle‐wheel” assisted percolative mechanism. Onset of metallic silver in the single crystals is documented, seemingly dependent on thermal pre‐history, mosaic structure and chemical synthesis. Possible mechanisms explaining this effect, comprising disproportionation or photo‐decomposition, are suggested.     

Unique morphologies of zinc oxide synthesized by thermal decomposition and co‐precipitation routes: Ultraviolet absorption and luminescence characteristics

Two facile and efficient methods, to synthesize zinc oxide (ZnO) particles with different morphologies, have been reported here. Thermal decomposition route yielded micron sized irregular shaped ZnO particles. While co‐precipitation method rendered transparent flakes which then transformed to hexagonal discs with relatively more uniform size and shape. These hexagonal discs were further converted to the cone type morphology when hexamethylenetetramine was added in the precursor solution. However, spherical type ZnO nanoparticles were obtained by incorporating polyvinyl alcohol during co‐precipitation strategy. XRD confirmed the formation of wurtzite structure in all the samples. FTIR spectroscopy revealed the presence of ZnO characteristic peaks. Moreover, 3‐D directional growths and the presence of UV‐Vis broadband multi‐absorption peaks, and green to orange photoluminescence emissions confirmed the potential application of the synthesized ZnO particles in various piezoelectric and luminescence applications.

     

1,6‐Hexanediammonium Dihydrogendecavanadate Dihydrate, (H3N—(CH2)6—NH3)2H2V10O28 · 2 H2O

The crystal structure of (H₃N—(CH₂)₆—NH₃)₂H₂V₁₀O₂₈ � 2 H₂O consists of dihydrogendecavanadate anion with C_i symmetry, two 1,6‐hexanediammonium cations and two water molecules. The structure has a P space group symmetry with one of the cations in special position; this cation is disordered. The polyanion of most usual protonation type is similar as formed in other known dihydrogendecavanadates.     

Room temperature epitaxial growth of (001) CeO2 on (001) LaAlO3 by pulsed laser deposition

The room temperature epitaxial growth of CeO₂ on lattice matched (001) LaAlO₃ substrates by using pulsed laser deposition (PLD) method under various oxygen partial pressure (Po₂) is demonstrated. X‐ray diffraction analysis with 2‐Theta/rocking curve/Phi‐scan, cross‐sectional transmission electron microscopy with selected‐area diffractions are used to characterize structural of grown films. The epitaxial (001) CeO₂ can be achieved at room temperature under Po₂ less than 2 × 10⁻³ Torr. The best quality of grown film is obtained under Po₂ = 2 × 10⁻⁵ Torr and degraded under Po₂ = 2 × 10⁻⁶ Torr due to oxygen deficiency in structure. The epitaxial relationship between CeO₂ and LAO is confirmed to be (001)CeO₂ //(001)LAO, [100]_CeO2//[110]_LAO and [010]_CeO2//[10]_LAO. No obvious reduction reaction occurred, from Ce⁺⁴ turned into Ce⁺³ states, as reducing oxygen partial pressure during growth by PLD.     

Research on the multi‐crystalline structure in sapphire grown by Kyropoulos technique

The macroscopic distribution of multi‐crystalline structure (MCS) in a sapphire boule grown by Kyropoulos technique was characterized using polariscope. The morphology and texture of subgrains from , and orientations were investigated using Synchrotron radiation white‐beam topography technique. The morphology of subgrains was found to be diverse from crystallographic orientation. The relative angles between subgrains are smaller than 1°. The defect structure on a basal‐plane specimen from the lower part of the “shoulder” was examined by X‐ray rocking curve and chemical etching technique. It was found that the defect concentration changes drastically near MCS center. The nature of spatial distribution of MCS and the defect distribution near MCS in a grown boule was discussed in detail.     

Precipitates originating from tungsten crucible parts in AlN bulk crystals grown by the PVT method

In order to evaluate the possible involvement of crucible materials in the growth of AlN bulk crystals grown by physical vapor transport, we applied growth conditions with a high vertical thermal gradient and hence high supersaturation of aluminum vapor. Under these conditions, precipitates formed causing diffuse grayish substructures at the initial growth interface and in the crystal body, decorating dislocations. Electron microscopy studies revealed that the precipitates are elongated, single‐phase particles with sizes of 50–500 nm of commensurate structure, oriented along the <110> direction. Chemical analysis of the precipitates showed tungsten as well as carbon and oxygen. The lattice parameters of the precipitates are in close agreement to hexagonal tungsten hemicarbide (W₂C). The possible transport from the tungsten parts and its conversion into tungsten hemicarbide precipitates is discussed. We thus conclude that the W₂C precipitates may contribute to the decoration of dislocations, even in growth with moderate thermal gradients.     

Crystal growth experiments in the systems Ni2MSbO6 (M = Sc,In) using chemical vapour transport reactions: Ni2InSbO6 and NiSb2O6 crystals in the millimetre range

Endothermic chemical vapour transport (CVT) reactions of Ni₂MSbO₆ (M = Sc, In), using a temperature gradient of 1313 → 1233 K and HgCl₂, HgBr₂, PtCl₂ or TeCl₄ as transport agents, led to growth of Ni₂InSbO₆ single crystals in the millimetre range, whereas in the case of Ni₂ScSbO₆ an incongruent dissolution of the solid in the source region was observed, leading to the formation of single crystals of the ternary phase NiSb₂O₆ in the sink region. The crystal structures of the obtained crystals were refined from single crystal X‐ray data with high precision [Ni₂InSbO₆: R3, Z = 3, a = 5.21640(10) Å, c = 14.0142(3) Å, 1279 structure factors, 33 parameters, R[F² > 2σ(F²)] = 0.0189; NiSb₂O₆: P4₂/mnm, Z = 2, a = 4.63910(10) Å, c = 9.2182(2) Å, 500 structure factors, 19 parameters, R[F² > 2σ(F²)] = 0.0145]. Ni₂InSbO₆ crystallizes in a corundum‐related structure, NiSb₂O₆ in the trirutile structure type. Spontaneous polarization and the ferroelectric transition temperature were estimated from the atomic arrangement and cation displacement along the polar axis in Ni₂InSbO₆. Magnetic measurements on Ni₂InSbO₆ evidence an antiferromagnetic transition near T_N = 74 K, with significant magnetic frustration.     

Surface preparation of AB semiconductors (Cd3As2, Zn3As2, Cd3P2, Zn3P2) under ultra-high vacuum conditions

The UHV surface preparation of AB materials (crystals and thin films) has been monitored with XPS and AES. Clean and stoichiometric surfaces of AB crystals were prepared by means of low energy ion bombardment and subsequent low temperature annealing. Stoichiometric Cd₃As₂ and Zn₃P₂ thin films with very low amounts of C and O were deposited by the evaporation of bulk material in the UHV. The quality of prepared AB crystal and thin film surfaces was sufficient to carry out density of states investigations (UPS, RELS) with success.     

Experimental investigations of buoyancy-driven convection in vertical (BixSb1−x)2Te3 molten zones

Experimental results for various states of buoyancy driven flow in vertical (Bi_0.23Sb_0.75)₂Te₃ molten zones with covered surface are presented. Critical thermal wall Rayleigh numbers Ra for the onset of time-dependent convection have been determined by means of temperature measurements. The stability diagram obtained for the existing buoyancy driven convection shows the increase of Ra with increasing aspect ratio. This relation is also known from other crystal growth configurations and is due to the damping influence of container walls. At the beginning in the oscillatory region of convection extremely long periods of oscillation (maximum 850 s) were observed, which are caused by another mechanism than periods (25 … 37 s) registered at increasing melt heights. Furthermore, Bi_0.5Sb_1.5Te₃ crystals were grown by using the vertical zone melting technique. The microscopic striations observed in the grown crystals correlate exactly with the temperature signals caused by time dependent convection. However, the fluctuations of the tellurium distribution in axial direction measured by scanning the Seebeck coefficient are presumably generated by unsteady solutal convection during growth.     

X-Ray diffraction and IR-spectroscopic studies of UO2(n-C3H7COO)2(H2O)2 and Mg(H2O)6[UO2(n-C3H7COO)3]2

Single crystals of UO₂(n-C₃H₇COO)₂(H₂O)₂ (I) and Mg(H₂O)₆[UO₂(n-C₃H₇COO)₃]₂ (II) are synthesized. Their IR-spectroscopic and X-ray diffraction studies are performed. Crystals I are monoclinic, a = 9.8124(7) Å, b = 19.2394(14) Å, c = 12.9251(11) Å, β = 122.423(1)°, space group P2₁/c, Z = 6, and R = 0.0268. Crystals II are cubic, a = 15.6935(6) Å, space group $Pa\bar 3$ , Z = 4, and R = 0.0173. The main structural units of I and II are [UO₂(C₃H₇COO)₂(H₂O)₂] molecules and [UO₂(C₃H₇COO)₃]^? anionic complexes, respectively, which belong to AB ₂ ⁰¹ M ₂ ¹ (I) and AB ₃ ⁰¹ (II) crystal chemical groups of uranyl complexes (A = UO ₂ ²⁺ , B ⁰¹ = C₃H₇COO^?, and M ¹ = H₂O). A crystal chemical analysis of UO₂ L ₂ · nH₂O compounds, where L is a carboxylate ion, is performed.     

Effect of chlorine ion on the crystalline and photocatalytic activity of BiOCl for the degradation of Rhodamine B

Two kinds of layer‐structured BiOCl photocatalysts (BiOCl‐01 and BiOCl‐02) were synthesized using NaBiO₃ and HCl as the raw materials, and KCl as the Cl⁻ conditioning agent. These photocatalysts were characterized by X‐ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and ultraviolet visible diffuse reflectance spectra (DRS) measurements. The effects of chlorine ion in the reaction solutions on the crystalline of BiOCl and photodegradation of Rhodamine B (RhB) under 365 nm and 530 nm monocharomatic light irradiation were investigated. The XRD spectra confirmed the formation and purity of BiOCl photocatalysts, revealed that Cl⁻ ion existed in the preparation solution restrained the growth of BiOCl and influenced the surface configuration. The TEM and HRTEM analysis gave the similar results with XRD. The band gaps of BiOCl‐01 and BiOCl‐02 were estimated about 3.19 and 3.29 eV, respectively. The photocatalytic degradation results of RhB under 365 nm showed that the photocatalytic activity of BiOCl‐02 was better than that of BiOCl‐01, and the main active species were h⁺ and . Meanwhile, the photosensitized results of RhB under 530 nm indicated that the photosensitized activity of BiOCl‐01 and BiOCl‐02 was similar, and the main active species was .     

Single crystal growth of La2(SO4)3 · 9 D2O

Single crystals of La₂(SO₄)₃ · 9 D₂O were grown from saturated D₂O solutions. According to X-ray diffraction measurements, the crystals have a hexagonal structure with unit cell parameters a = 10.996 Å and c = 8.077 Å (space group C–P6₃/m). Several physical properties were also determined (density, refractive indices, dielectric constants, specific heat, coefficient of linear expansion, microhardness).     

Absorption spectrum of octahedral CoCl4(H2O)2 units in [(CH3)3NH]CoCl3·2H2O single crystal

The optical absorption spectrum of the octahedral moiety CoCl₄(H₂O)₂ in single crystal [(CH₃)₃NH]CoCl₃·2H₂O has been studied at room and liquidair temperatures. The observed ambient bands at 6800, 16,300, and 19,000 cm^–1 have been assigned, respectively, to the transitions⁴ T ₁(F) ⁴ T ₂(F),⁴ A ₂(F), and⁴ T ₁ (P). The crystal field parameters evaluated areD _q =B=850 cm^–1, andC=4.63B. At liquid-air temperatures the⁴ T ₁(P) band is seen to split into the expected four components ₇, ₈, ₈, and ₆, due to spin-orbit coupling, and the coupling coefficient was computed to be 525 cm^–1.     

The OD Structure of Dinitrosylcobalt Chloride, [Co(NO)2Cl]2

The OD groupoid family of the structure of dinitrosylcobalt chloride, [Co(NO)₂Cl]₂, is characterized by the symbol: The OD groupoid family of the structure is deduced from the observed arrangement of points in reciprocal space, the symmetry of the intensity distribution and the systematic absences. The structure is built of OD layers of one kind. The determination of the structure of the ordered orthorhombic form (MDO₂) has been determined from Weissenberg data obtained by JAGNER and VANNERBERG refined with OD full-matrix least-squares methods, based on a total of 150 reflections and anisotropic temperature coefficients. An R value of 0.13 has been obtained. The assumption of JAGNER that the structure is composed of dimers has been found to be justified.     

Transport Coefficients of (Bi1-xSbx)2Se3 Single Crystals

(Bi_1-xSb_x)₂Se₃(x = 0.0 to 0.2) single crystals were prepared using a modified Bridgman method. Measurements of the Hall coefficient R_H, electrical conductivity σ and Seebeck coefficient α showed that incorporation of the antimony atoms into the Bi₂Se₃ crystal lattice results in an increase in the free electron concentration for a low antimony content, whereas the free electron concentration is suppressed in the range of a high antimony content. This effect is explained qualitatively by changes in the concentrations of point defects in the (Bi_1-xSb_x)₂Se₃ crystals. We asume that the substitution of Bi atoms by Sb atoms results in a decrease in the concentration of Se vacancies V and antisite defects Bí_Se. The course of the dependences of In (R_Hσ) vs In T manifests that in the temperature region of 100–400 K transport properties of the studied crystals are characterized by a mixed transport mechanism of free carriers, mainly on acoustical phonons and ionized impurities.     

The precipitation of barium chromate from aqueous solution (with rapid mixing): Kinetics of the crystal growth

The kinetics of precipitation of barium chromate from well-stirred aqueous solutions of initial solute concentrations C₀ = 0.0001 to 0.0010 M (supersaturations 8 to 80) was studied at 25 °C by conductivity measurements and chemical analysis. Nucleation occurred during induction periods and regular crystal growth then took place onto the crystallites formed during the induction periods. The crystal growth was rate-controlled, in this range, by the rate of deposition of metal salt ions onto the growing crystal surfaces. This rate, at any time, then depended on both the overall surface area (A_t) and on the residual excess solute concentration (ΔC_t) in solution according to the relation, the growth rate expressed in terms of degree of crystallisation was then The rate constant (K_α) for the crystallisation of barium chromate at 25 °C was 1.5 10⁶ sec⁻¹ M⁻².     

The structure of N-Pyrid-2-yl-iminotriphenylphosphorane,C23H19N2P

M_r = 353.9, monoclinic, P 2₁/c, a = 11.371(4), b = 11.391(5), c = 14.699(11) Å, β = = 97.78(2)⁰, Z = 4, V = 1888.6(6) ų, D_x = 1.28 Mgm⁻³, final R = 0.052 for 2360 independent reflections excluding those with |F₀| < 5 σ(F₀). Intensities were measured with an automatic diffractometer. The PN C- part of the molecule is nearly coplanar with the pyridinring (torsion angle 6.4°). The P atom and the N(2) atom of the pyridinring overlap with their van der Waals spheres and have nearly the position with the maximum of steric hindrance. This conformation of the molecule is the consequence of a conjugation between the Ph₃P=N-group and the N-standing pyridine ring as well as of an attraction between the P atom and the N(2) atom.     

Absorption and ionic conductivity of oxygen-containing SrF2 crystals

An absorption band at 3644 cm⁻¹ is caused by isolated OH⁻ ions. O⁻ ions cause an absorption band at 213 nm the oscillator strength of which is 0.020. Charge-compensation of O⁻ ions is effected by F⁻ ion vacancies (F). As for CaF₂ crystals there occur monomers and dimers of [O⁻ – F] complexes. The mass action constants of association of F with oxygen centres are K_AD = ⅓ exp (4.28 – 0.82 eV/kT) for [O⁻ – F], K_AT = 4 exp (17.4 – 1.25 eV/kT) for [2 O⁻ – F] and K_AQ = exp (4.2 – 0.89 eV/kT) for [2 O⁻ – 2 F].     

The effect of B2O3 on the solubility of (YSmLuCa)3(FeGe)5O12 garnet in PbO-B2O3 flux

The paper deals with the solubility of (YSmLuCa)₃ (FeGe)₅O₁₂ garnet in PbO—B₂O₃ flux. An anionic model explaining the effect of B₂O₃ on the solubility of rare earth garnet is suggested. This model is based on the assumption that PbO in the melted mixture of PbO, B₂O₃, Fe₂O₃, R₂O₃, CaO, GeO₂ dissociates into Pb²⁺ and O²⁻. The oxygen anions react with the other oxides under the formation of BO₃³⁻, FeO₃³⁻, RO₆⁹⁻, CaO₂²⁻ and GeO₃²⁻ anions, until the equilibrium is established. The garnet is dissociated into the anions mentioned above. The validity of the model is verified by an agreement of the experimentally determined saturation temperatures of the melts for LPE of garnet layers with the Arrhenius-type expression of the solubility product of garnet where x_i denotes the equilibrium concentrations of the anions in the melt and x° is the Ge content of the garnet film.     

OD interpretation of the crystal structure of lithium tellurite,Li2TeO3

The OD groupoid family of the structure of lithium tellurite, Li₂TeO₃, is characterized by the symbol: . The OD groupoid of the structure is deduced from the observed arrangement of points in reciprocal space, the symmetry of the intensity distribution and the systematic absences. The structure is built of OD layers of one kind. Any OD layer is idendical to a Li₂TeO₃ double sheet. The assumption of Folger that the structure is an OD structure has been found to be justified.