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A series of BaO:RxOy:CuO materials has been prepared where R=Y, La, Ce, Pr, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. They have been characterized by X-ray powder diffraction methods. All BaR2CuO5 phases, commonly referred to as the “green phases”, are orthorhombic with space group Pbnm(62) and are isostructural. These single phase materials could be prepared with most lanthanides, except for La, Ce, Pr, Nd and Tb. Possible reasons for the exceptions are discussed. Both La and Nd tend to form a brown solid solution of Ba2+2xR4-2xCu2-xO10-2x with a tetragonal space group of P4/mbm(127). The major phases found in the Ce, Pr and Tb compositions are the perovskite-related structures BaRO3, and in the Pr case, Ba2PrCu3O6+x as well. The cell parameters of the green phase materials increase progressively from the Lu compound to the Sm compound: a ranges from 7.0506(6) to 7.2754(4) Å, b from 12. 0534(8) to 12. 4029(7) Å, c from 5.6099(5) to 5. 7602(3) Å, and the cell volume from 476.75(6) to 519.78(4) Å3. A correlation of the crystallographic data with the size of the R elements is given.
A powder diffraction method was applied to the quantitative analysis of amorphous silica in several quartz powders. Two calibration methods, i.e., direct analysis and the standard addition method were examined. Calibration mixtures were made by mixing a standard silica gel powder ground to under 5 μm particle size with a matrix quartz powder which was ground to 10 to 40 μm particle size and treated with NaOH solution to remove the amorphous phase caused by grinding. Intensity of the amorphous halo was measured at 23.0° 2θ, and the background intensity at 53.0° 2θ was subtracted. Linear calibration curves were obtained over the ranges of 0 to 50 wt% by direct analysis and 0 to 20 wt% by standard addition methods, respectively. The analytical results obtained by the two calibration methods were in good agreement with each other. The relative standard deviations for 4.3 wt% of amorphous silica were 4.6% by the direct analysis and 5.4% by the standard addition method. These methods were successfully applied to a correction of reference intensity ratios (RIR) for several quartz powders containing amorphous silica. After the correction for amorphous content, the relative standard deviations of the RIR values for quartz powders became smaller.
Crystals of sodium copper oxalate dihydrate [Na2Cu (C2O4)2.2H2,O] were obtained by the gel method, from solutions of oxalic acid and copper chloride. The crystals form blue needles with idiomorphic faces of brilliant luster, permitting goniometric measurements and the determination of the morphology with the aid of crystallographic parameters. Optically the crystals are biaxial negative, 2V = 38°, with a weak dispersion r<v. The orientation of the indicatrix was determined using a universal stage.
Crystals of sodium copper oxalate dihydrate, Na2Cu (C2O4)2.2H2O, were apparently first obtained in 1929 by Riley. Gleizes et al. (1980) undertook a preliminary crystallographic study of crystals obtained by a different technique from Riley's. In the first case, a solution of 33.5 g/L of sodium oxalate was heated and then poured gradually into a nearly saturated solution of copper sulfate until slight turbidity appeared. The turbidity was eliminated and the solution clarified by the addition of a little more sodium oxalate solution. In this way Riley obtained a dark blue solution which after filtration yielded extremely fine sky-blue needle-like crystals, rarely more than 8mm long. In the method of Gleizes et al. (1980), copper oxalate was dissolved in an aqueous solution of sodium oxalate; those authors observed complete dissolution when the molar ratio of sodium oxalate to copper oxalate was near 2. By evaporating the solution, they obtained long, prismatic crystals whose crystallographic constants they determined.
In order to obtain crystals large enough for further crystallographic study, we set out to produce crystals of sodium copper oxalate by the gel method (Triché, 1984). We found that slow crystallization did encourage the formation of large crystals.
The unit cell dimensions of minerals in the smectite group, regular and random mixed-layer groups, and halloysite shown in the Mineral Powder Diffraction File (1986) have been refined by least-squares analysis in the hexagonal system with a primitive lattice with indices restricted to hk or 00l reflections. Trioctahedral minerals have larger a unit-cell dimensions than dioctahedral minerals.
Observed powder diffraction data for two tetracyclines were interpreted with the aid of calculated patterns based upon the crystal structures determined from a single crystal of the same batch for each compound. The results consist of high quality standard powder patterns with the usual supporting data.
Since the discovery of the superconductivity in Ba2YCu3 O7-x, the system Ba-Y-Cu-O has generated vast interest. The presence and the properties of the intermediate phases were examined, and the existence of the BaY2O4 phase was confirmed.
We have determined the crystal structure of this material from powder data; it is orthorhombic, Pnma (no 62) with a = 10.394(3) Å, b = 3.450(1) Å, c = 12.113(4) Å, isotypic with SrY2O4 (CaFe2O4-type). The observed and calculated intensity values are reported together with the powder diffraction data, obtained both by Guinier and diffractometer methods.
High quality powder diffraction data were obtained from a specimen containing inseparable impurities, by using single crystal precession photographs to explore all possible reflections for the mineral being studied. In this manner it is acceptable to ignore weak reflections that do not index on the unit cell and that are not observed on the single crystal photographs. Triphylite is given as an example.
Zr(MoO4)2 molybdate has been synthesized by solid state reaction. Single crystals were obtained by hydrothermal synthesis. Corrected crystal data are: monoclinic, a = 11.4309 (3), b = 7.9376 (2), c = 7.4619 (2) Å and β = 122.323 (2)°, V = 572.13 (6) /cm3 (5), Dx = 4.770 g/cm3. Powder diffraction data are reported.
Thirteen isotypic tellurates having the stoichiometries MIBaNbTe2O9 and BaNbTe2O9, with MI = Li,Na,K,Rb,Ag and MII = Mg,Ca,Sr,Ba,Cu,Zn,Cd,Pb, have been synthesized by solid state reaction. Single crystals of KBaNbTe2O9 were obtained. The compounds crystallize in the orthorhombic space group P212121 . Unit-cell parameters for the 13 compounds and powder diffraction patterns for three representative compounds, KBaNbTe2O9, Ba1.5NbTe2O9 and Cd0.5BaNbTe2O9, are given.
Wolfeite (Fe0.59Mn0.40Mg0.01)2PO4(OH) from the Hagendorf-Sud pegmatite, Bavaria, Federal Republic of Germany, yields unit-cell parameters of: a = 12.319(1), b = 13.280(2), c = 9.840(1) Å and β = 108° 24(1). Dmeas. = 3.82(2); Dcalc. = 3.88. An indexed powder diffraction pattern is given.
Fourteen reference patterns of oxide ceramics are reported. Included in the fourteen reference patterns are data for nine high critical temperature super-conducting oxide related phases: (BaCuEr2O5, Ba2Cu3EuO7, BaCuGd2O5, Ba2Cu3GdO7, Ba2.4Cu5La4O13, Ba1.9cu3La1.1O7, Ba2Cu3SmO7 and (Ba0.4Sr0.6)2Cu3 YO7). The general methods of producing these X-ray powder diffraction reference patterns were described previously in this journal (Vol. 1, No. 1, pg. 40 (1986)). The symbols used in this article are defined in the PDF cards.