The new phase LaCr(NO3)6·12H2O was synthesized from a nitric acid solution. The symmetry is trigonal with the parameters a=10.9564(4) Å and c=16.835(1) Å [V=1750.2(2) Å3, space group R-3]. The thermal decomposition, studied by temperature-dependent X-ray powder diffraction and thermogravimetry, gave successively the cubic phase LaCr(NO3)6·6H2O [a=12.301(1) Å, space group P213] and the chromate(V) LaCrO4. The reduction of LaCrO4 to LaCrO3 occurred at a temperature depending on the oxygen pressure in the reaction atmosphere.

A quantitative simultaneous determination method by X-ray powder diffractometry is described for calcium sulfate and calcium carbonate in airborne dusts. In order to eliminate the mutual interference among diffraction peaks, and to avoid the presence of the hydration isomers of calcium sulfate, dust samples were heated at 350°C for 2 h. To reduce the errors due to the difference-in crystallinity between the standard materials and the samples, the synthesized calcium sulfate anhydrate (anhydrite) was heated to such an extent that the half-width of the 002,020 peak was identical with that of the anhydrite in pretreated dust samples. Standard calcium carbonate (calcite) was ground until the half-width and the orientation index of the 104 peak of calcite was identical with that of the calcite in dust samples. Linear calibration curves were obtained throughout the range of 0 ∼ 30 wt% for anhydrite and the range of 0 ∼ 10 wt% for calcite, respectively. The determination limits were 0.2 wt% for anhydrite and 0.3 wt% for calcite. Relative standard deviations were 3.4 % for 8.0 wt% of anhydrite and 1.8% for 5.4 wt% of calcite. The present method is applicable to determination of calcium sulfate and calcium carbonate in actual dust samples.

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.

A previously manually operated film comparator used to evaluate Guinier films has been automated as a film scanner of the flat film type. The film movement is controlled by a stepper motor and the intensity of the transmitted light is recorded as a function of position on the film. A personal computer controls the stepper motor and records the measurements of the transmitted light intensity. The data quality is judged from refinements of lattice constants for α-SiO2 and ZrO2. The powder pattern for Pb2Sr2Ho0.625Ca0.375Cu3O8 and a high temperature study of the thermal expansion of GeO2 are presented.

An external standard method using mica for angular calibration of powder diffractometers is described. This is useful especially when standard referee materials certified by the US National Institute of Standards and Technology are not accessible.

The complexes [C(NH2)3]3MF6, M = Cr, Fe have been isolated from aqueous solutions of the corresponding fluorides. The compounds are isostructural and crystallize in the cubic space group with a = 14.0667 (6) Å for M = Cr, a = 14.1246(8) Å for M = Fe and Z = 8. The MF63− anions are arranged as Na+ and Cl− in the NaCl lattice. Guanidinium cations are distributed on 24-fold general position.

The effects of sample transparency in a powder diffraction experiment are discussed, and formulas including effects from horizontal divergence are derived. It is shown that the classical formula by Alexander [L. E. Alexander J. Appl. Phys. 21, 126 (1950)] is only a limiting case for zero horizontal divergence. It is also shown that in some cases extinction effects can play a role. The impact of these effects on both the line profile as well as the integrated intensity and experiments illustrating these phenomena, are discussed.

Powder diffraction patterns have been calculated for nine isostructural rhombohedral M2(SO4)3 (M = Sc, Ti, V, Cr, Fe, Ga, Y, Rh, In) phases, and for four isostructural monoclinic M2(SO4)3 (M = V, Fe, In, Tl) phases. The pattern for monoclinic Fe2(SO4)3 is the first reported for this phase. Because structure data are available only for the two Fe2(SO4)3 polymorphs, the powder patterns of the other trivalent metal sulfates were approximated using the structure data of the isostructural Fe phases with the scattering factors and previously determined cell parameters of the various metal sulfates. These calculated patterns are termed an approximation by isostruduralism.

The calculated patterns were used to evaluate reference powder data for these phases in the Powder Diffraction File (PDF). All but two of the PDF patterns were found to differ substantially from the calculated patterns in the stronger peaks used for identification, and to be missing weak peaks that may be confused for impurities during phase identification.

A new diffraction pattern of the high-temperature and high-pressure polymorph Mg3(PO4)2-III (PDF 43-500) is given and indexed on the basis of a single-crystal structure refinement. It allows diffractogram indexing of the isostructural high-temperature and high-pressure form of Co3(PO4)2 (PDF 43-499).

The cubic Al18Ti2Mg3 phase (184 atoms/unit cell, Z = 8, space group Fdm) has been fabricated by reaction hot isostatic pressing. Quantitative energy dispersive X-ray analysis showed the phase to have nearly ideal stoichiometry. Interplanar spacings and diffraction peak intensities have been determined by X-ray diffraction. The experimental data show good agreement with the pattern calculated using atomic site positional parameters for A118Cr2Mg3, confirming that A118Cr2Mg3 is the prototype for A118Ti2Mg3.

The construction and use of a captive inert atmosphere cell for the preservation of atmospherically sensitive samples during X-ray diffraction is described.

Based on analysis of its powder diffraction pattern, tetracycline hydrochloride is orthorhombic; the space group is probably P212121(19) or P21212(18). Indexed powder data and refined cell parameters are presented.

The aim of any diffraction experiment is to obtain reproducible data of high accuracy and precision so that the data can be correctly interpreted and analyzed. Various methods of sample preparation have been devised so that reproducibility, precision and accuracy can be obtained. The success of a diffraction experiment will often depend on the correct choice of preparation method for the sample being analyzed and for the instrument being used in the analysis.

A diffraction pattern contains three types of useful information: the positions of the diffraction maxima, the peak intensities, and the intensity distribution as a function of diffraction angle. This information can be used to identify and quantify the contents of the sample, as well as to calculate the material's crystallite size and distribution, crystallinity, and stress and strain. The ideal preparation for a given experiment depends largely on information desired.

The modal analysis of samples belonging to the zeolite-rich pyroclastic formation named “Neapolitan yellow tuff” (Central and Southern Italy) has been determined by full-profile refinement of X-ray powder diffraction (XRPD) data using a combined Rietveld–RIR method. The quantitative analysis and especially the zeolite content is a profitable source for geo-petrographic and genetic considerations and as well an essential source to assess the physical and chemical properties of the bulk material for a feasible use in industrial applications. Albeit a wealth of methods are used for the quantitative determination of zeolite content in pyroclastites they all fail for lack of accuracy as far as concerns the absolute standard deviation of the quantitative data. The outstanding outcomes achievable by using the Rietveld method make it as the most promising technique to fulfill this lack. The glass content in each sample is calculated by a combined Rietveld–RIR method in which a known amount of an internal standard is added to the mixture to rescale the Rietveld refined weight fractions into absolute values. Then, it is reasonable to designate this method as an external method according to the definition given by Hill and Howard (1987). Its counterpart is the internal method developed by Riello etal. (1995a,b). Other techniques such as the addition method and the background scattering volume calculation are developed to accomplish a further determination of the glass content. The results are compared to the values obtained from the Rietveld–RIR analysis. These experimental methods yield an over-estimation of the amorphous phase because the incoherent scattering contribution (air, absorption, sample holder, Compton scattering) is accounted for as the amorphous fraction itself. The glass content of each sample acquired from the Rietveld–RIR refinement on the “raw data” is compared to that accomplished from the refinement of incoherent scattering subtracted data. In addition, some largely used XRPD quantitative techniques such as the external standard and RIR (reference intensity ratio) and the influence of the sample loading method are accounted for in an internally consistent comparison among different procedures of analysis.