Growth of Gallium Orthophosphate Single Crystals under Hydrothermal Conditions

Gallium orthophosphate (GaPO₄) single crystals have been grown from phosphoric acid solutions under hydrothermal conditions. The crystals have been studied in terms of twinning because of the strong effect of this structural defect on the piezoelectric properties. The growth rates of individual faces have been compared to each other by considering the dipyramidal habit of the grown crystals.     

CuInOVO4 – Einkristalle eines Kupfer(II)‐indiumoxidvanadats durch Oxidation von Cu/In/V‐Legierungen

CuInOVO₄ – Single Crystals of a Copper(II) Indium Oxide Vanadate by Oxidation of Cu/In/V Alloys Red‐brown crystals of the new compound CuInOVO₄ (monoclinic, P2₁/c, a = 879.3(2) pm, b = 615.42(6) pm, c = 1526.2(2) pm, β = 106.69(2)?, Z = 4) were prepared by the reaction of Cu/In/V alloys with oxygen. The investigated crystals were twins by pseudo‐merohedry with a (001) twinning plane. The structure contains isolated Cu₄O₁₈‐groups consisting of trans edge sharing CuO₆‐octahedra. Interconnection of the groups by [In₄O₁₆]‐ribbons running along [010] which are built of edge‐ and corner‐sharing InO₆‐octahedra results in the formation of slabs perpendicular to the c‐axis. The slabs are linked to a threedimensional framework by VO₄^3– groups. The structure may be derived from a cubic closest packing of the oxygen atoms with copper and indium atoms in the octahedral and vanadium atoms in the tetrahedral vacancies.     

Texture transition in Al–Mg alloys: effect of magnesium

ABSTRACT

The evolution of deformation texture and microstructure in commercially pure Al (cp-Al) and two Al–Mg alloys (Al–4Mg and Al–6Mg) during cold rolling to a very large strain (true strain ε_t? ≈?3.9) was investigated. The development of deformation texture in cp-Al, after rolling, can be considered as pure metal or Copper-type, which is characterised mainly by the presence of Cu {112}<111>, Bs {110}<112> and S {123}<634> components. The deformation microstructure clearly indicates that deformation mechanism in this case remains slip dominated throughout the deformation range. In the Al–4Mg alloy, the initial slip mode of deformation is finally taken over by mechanism involving both slip and Copper-type shear bands, at higher deformation levels. In contrast, in the Al–6Mg alloy, the slip and twin mode of deformation in the initial stage is replaced by slip and Brass-type shear bands at higher deformation levels. Although a Copper-type deformation texture forms in the two Al–Mg alloys at the initial stage of deformation, there is a significant increase in the intensity of the Bs component and a noticeable decrease in the intensity of the Cu component at higher levels of deformation, particularly in the Al–6Mg alloy. This phenomenon indicates the possibility of transition of the deformation texture from Cu-type to Bs-type, which is concurrent with the addition of Mg. Using visco-plastic self-consistent modelling, the evolution of deformation texture could be simulated for all three materials.     

Synthesis,Crystal Structure and Charge Distribution of InGaZnO4. X‐ray Diffraction Study of 20kb Single Crystal and 50kb Twin by Reticular Merohedry

Synthesis of InGaZnO₄ at 20Kb and 50Kb produced a single crystal and a twinned crystal respectively. The X�ray diffraction crystal structure refinement (R1 = 0.015 and 0.019 respectively) and the Charge Distribution analysis are reported. Space group is R3m; cell parameters in hexagonal axes are a = 3.2990(2)Å, c = 26.1013(25)Å (20kb single crystal) and a = 3.3051(2)Å, c = 26.1029(19)Å (50kb twinned crystal). The cell volume is 246.01(3)ų and 246.94(3)ų respectively. The In is in regular octahedral coordination, whereas Ga/Zn are in trigonal bipyramid co‐ordination. Charge Distribution on cations (2.94 and 2.95 respectively vs. 3.0 for In, and 2.53 vs. 2.5 for Ga/Zn) shows that the structure is well refined. Charge Distribution on oxygens (—1.96 and —2.04 for O1 and O2, vs. —2.0) excludes the presence of valence unbalance effects. A possible structural role of the trigonal bipyramidal coordination is discussed.     

Alloying effect on grain-size dependent deformation twinning in nanocrystalline Cu–Zn alloys

Grain-size dependency of deformation twinning has been previously reported in nanocrystalline face-centred-cubic metals, which results in an optimum grain-size range for twin formation. Here, we report, for the first time in experiments, the observed optimum grain sizes for deformation twins in nanocrystalline Cu–Zn alloys which slightly increase with increasing Zn content. This result agrees with the reported trend but is much weaker than predicted by stacking-fault-energy based models. Our results indicate that alloying changes the relationship between the stacking-fault and twin-fault energy and therefore affects the optimum grain size for deformation twinning. These observations should be also applicable to other alloy systems.     

Packing considerations of 10‐oxa‐9‐boraphenanthrene derivatives

The crystal structures of three products of the reaction of 2‐phenylphenol and BCl₃ have been determined. The structures show intriguing packing patterns and an interesting case of pseudosymmetry. In addition, one of the two polymorphs has a primitive monoclinic crystal system, but it is twinned and emulates an orthorhombic C‐centred structure. Tris(biphenyl‐2‐yl) borate, C₃₆H₂₇BO₃, ( III ), crystallizes with only one molecule in the asymmetric unit. The dihedral angles between the planes of the aromatic rings in the biphenyl moieties are 50.47 (13), 44.95 (13) and 42.60 (13)°. The boron centre is in a trigonal planar coordination with two of the biphenyl residues on one side of the BO₃ plane and the remaining biphenyl residue on the other side. One polymorph of 10‐oxa‐9‐boraphenanthren‐9‐ol, C₁₂H₉BO₂, ( V a ), crystallizes with two almost identical molecules (r.m.s. deviation of all non‐H atoms = 0.039 Å) in the asymmetric unit. All non‐H atoms lie in a common plane (r.m.s. deviation = 0.015 Å for both molecules in the asymmetric unit). The two molecules in the asymmetric unit are connected into dimers via O—H...O hydrogen bonds. A second polymorph of 10‐oxa‐9‐boraphenanthren‐9‐ol, ( V b ), crystallizes as a pseudo‐merohedral twin with two almost identical molecules (r.m.s. deviation of all non‐H atoms = 0.035 Å) in the asymmetric unit. All non‐H atoms lie in a common plane (r.m.s. deviation = 0.012 Å for molecule 1 and 0.014 Å for molecule A). Each of the two molecules in the asymmetric unit is connected into a centrosymmetric dimer via O—H...O hydrogen bonds. The main difference between the two polymorphic structures is that in ( V a ) the two molecules in the asymmetric unit are hydrogen bonded to each other, whereas in ( V b ), each molecule in the asymmetric unit forms a hydrogen‐bonded dimer with its centrosymmetric equivalent. 9‐[(Biphenyl‐2‐yl)oxy]‐10‐oxa‐9‐boraphenanthrene, C₂₄H₁₇BO₂, ( VI ), crystallizes with four molecules in the asymmetric unit. The main differences between them are the dihedral angles between the ring planes. Apart from the biphenyl moiety, all non‐H atoms lie in a common plane (r.m.s. deviations = 0.026, 0.0231, 0.019 and 0.033 Å for molecules 1, A, B and C, respectively). This structure shows pseudosymmetry; molecules 1 and A, as well as molecules B and C, are related by a pseudo‐translation of about in the direction of the b axis. Molecules 1 and B, as well as molecules A and C, are related by a pseudo‐inversion centre at ,,. Neither between molecules 1 and C nor between molecules A and B can pseudosymmetry be found.     

Orientation-dependent microstructure development during high-rate shear deformation of copper

ABSTRACT

The microstructure transformations in copper subjected to high-rate deformation via dynamic channel angular pressing (DCAP) have been examined after one and four DCAP passes using electron backscattering diffraction. The focus was on the interrelation between microstructure and texture evolution and on the role of deformation twinning in these processes. During the first pass, a mesoscopic banding is shown to be the main mechanism of grain fragmentation, while the texture is qualitatively similar to that of face-centered cubic metals subjected to equal channel angular pressing, including the presence of characteristic texture components C, A₁ and A₂. A correspondence between structural elements and texture components occurs. Specifically, the mesobands have orientations near either an A₁ or A₂ ideal orientation, whereas the matrix has an orientation near C. Inside the A₁-bands, microtwins with orientations near A₂ are observed. Detailed analysis of the A₂-bands suggests that they may be of twinning origin. Similar orientation dependence of microstructure, though on a much finer scale, is observed after four DCAP passes. Based on the microstructure examination, it was suggested that mesoscopic banding together with deformation twinning continue to be principal mechanisms of grain refinement until the fourth pass, resulting in the formation of ultrafine-grained structure.     

Redetermination of NaGdS2, NaLuS2 and NaYS2

The title structures NaGdS₂ (sodium gadolinium sulfide), NaLuS₂ (sodium lutetium sulfide) and NaYS₂ (sodium yttrium sulfide) were redetermined in order to improve the structural information available for the family of group 1 and thallium rare earth sulfides, which are isostructural with the rhombohedral α‐NaFeO₂ structure type. In particular, the present investigation has been directed at the rhombohedral sodium rare earth sulfides. The observed dependence of the fractional coordinate z(S²⁻) on the identity of the rare earth element in the newly determined structures is in agreement with the known structures of the potassium and rubidium analogues. Crystals of NaGdS₂ and NaLuS₂ display obverse–reverse twinning.     

Application of the crystallographic orbit analysis to the study of twinned crystals. The example of marcasite

The continuity of a substructure across the interface is considered a necessary condition for the formation of a twin. The application of the analysis of the eigensymmetry of crystallographic orbits to the derivation of this structural continuity is briefly reviewed and applied to the analysis of the {101} twin in marcasite. This analysis shows that one fourth of the structure, but half of the substructure near the composition surface, is common to the two orientations realized in the twin, the operation mapping the common atoms in the twinned domains being an n‐glide occurring every one fourth of the period along the direction quasi‐perpendicular to the twin plane. The existence of this significant common substructure justifies and explains the formation of the twin.     

Polymorphism of dinitro[tris(2‐aminoethyl)amine]cobalt(III) chloride

Three polymorphs of bis(nitrito‐κN)[tris(2‐aminoethyl)amine‐κ⁴N,N′,N′′,N′′′]cobalt(III) chloride, [Co(NO₂)₂(C₆H₁₈N₄)]Cl, have been structurally characterized in the 100–300 K temperature range. Two orthorhombic polymorphs are related by a solid‐state enantiotropic order–disorder k2 phase transition at ca 152 K. The third, monoclinic, polymorph crystallizes as a nonmerohedral twin. In the structure of the high‐temperature (300 K) orthorhombic polymorph, the Co^III complex cation resides on a crystallographic mirror plane, whereas the Cl⁻ anion occupies a crystallographic twofold axis. In the unit cell of the monoclinic polymorph, the cationic Co^III complex is in a general position, whose charge is balanced by two halves of two Cl⁻ anions, each residing on a crystallographic twofold axis.