The analysis of crystalline organic phases by X-ray powder diffraction presents special problems, beyond those typically associated with inorganic materials. The large unit cells often associated with organic compounds, combined with the low symmetry of the structures, give rather complicated diffraction patterns that contain many low angle lines. The Bragg–Brentano geometric arrangement employed in most commercial diffractometers gives maximum (d-spacing error at low diffraction angles. This geometry, in turn, means that not only can the large (d-spacing data be of poor quality, but also that much of the low angle data required for the indexing of the pattern is subject to large errors.

Plane analytical geometry has been used to derive formulas of peak shifts due to specimen geometry and beam divergence of X-ray diffractometers in a Seemann–Bohlin configuration. When the attenuated diffraction below the specimen surface is not considered, peak shifts depend on Bragg angle (θ), incident beam divergence (2α), curvature radius of the specimen surface (r), and the tilt angle of the specimen (ψ). Numerical results show that at any fixed Bragg angle value, the peak shift increases with 2α whatever the combination of r and ψ values are. Moreover, at any fixed value of both Bragg angle and beam divergence, the peak shift depends directly on |ψ| and inversely on |r|. Shifts of peaks have been compared on both goniometer circle (Δ2θS) and focusing circle (Δ2θP). The results show that when ψ>0, then (Δ2θS) is less than (Δ2θP). On the contrary, when ψ<0, then (Δ2θS) is greater than (Δ2θP). Both (Δ2θS) and (Δ2θP) increase when the Bragg angle is decreased under the same fixed set of ψ, 2α, and r values. These peak shifts are so high that lattice strains may be masked at either high values of |ψ| and 2α, or small |r| values.

New X-ray powder data and a refined cell for mellite are presented and evaluated in comparison with the current PDF 28-2001.

Improved powder X-ray diffraction (XRD) data for liottite and sacrofanite, two members of the cancrinite group of minerals, were obtained using a rotating anode diffractometer. The cell parameters of liottite are a = 12.8575(3), c = 16.0905(6) Å, and the space group is ; the strongest reflections are at 4.834(38), 3.783(12), 3.714(100), 3.312(91), 2.784(13), 2.682(26), 2.470(17), and 2.143(27) Å. The cell parameters of sacrofanite are a = 12.8945(4) and c =74.2128(37) Å, and the possible space groups are P63/mmc, P63mc, and ; the strongest reflections are at 11.18(23), 3.757(25), 3.723(100), 3.488(27), 3.302(62), 2.651(31), 2.645(30), and 2.149(18) Å. The new data include an increased number of indexed peaks and empirical formulae that differ from the reference data (PDF 29-1187 and PDF 35-653, respectively).

Plastic crystals, such as neopentylglycol, 2, 2-dimethyl-1,3-propanediol, that exhibit polymorphic behavior are emerging materials for thermal energy storage. The energy is stored isothermally in the γ phase, FCC, during solid-state phase transformations. This γ phase of NPG has been determined as an orientational disordered phase. The low temperature α phase structure, which is of great significance in the evaluation of lattice expansions and other parameters, was first determined in 1961. However, the reported unit cell dimensions and the intensities of the reflections led to erroneous indexing of the powder patterns in binary systems. The α phase structure is redetermined here as monoclinic, M= 104.15 amu, space group P21/n (an alternate setting of , space group No. 14), a = 5.979(1)Å, b= 10.876(2)Å, c=10.099(2)Å, β=99.78(1)°, V=647.2(2)Å3 at 20°(± 1)C, Dx= 1.069 g cm s−3 for Z=4. In this paper the redetermined structure of the α phase of NPG is presented in projections of the atomic positions, in tables, and in calculated powder pattern and these results are compared with those reported by others. The powder patterns obtained from the Bragg–Brentano diffractometer are compared with our calculated pattern from the single crystal data. The structural parameters of the high temperature phase of NPG as determined by a Guinier diffraction system are also reported.

Eight phosphates and arsenates of manganese have been synthesized and examined using powder X-ray diffraction in order to update or extend the current powder diffraction data files. The studied compounds are MnPO4·H2O, MnAsO4·H2O, LiMnPO4(OH) LiMnAsO4(OH), LiMnAsO4, Mn2As2O7) MnAsO4, and Mn(PO3)3. The powder patterns have been indexed and the cell data are reported.

Three members of the family [CuC15H11N3)X2]·nH2O [X−=NCO (n=1), NCSe and N3 (n=ø)], C15H11N3=2,2′:6′,2″ – terpyridine (terpy), have been prepared by reaction in solution. Crystal data determined widi the aid of single crystal methods, powder diffraction data, and densities determined by flotation methods are presented.

A conventional Bragg-Brentano type diffractometer was equipped with a stepping motor, a timer, and a scaler, and an MC68000 Motorola microprocessor which controls the diffractometer functions. The microprocessor was programmed to operate the diffractometer in a step-scanning mode, to check a datum and to communicate with a process control computer, e.g. a PDP 11/44 or a Micro VaxII computer.

Three orthovanadates ATh2(VO4)3with A = Li, Na, Ag have been synthesized by solid state reaction. Single crystals of AgTh2(VO4)3were obtained. This compound is isotypic with sheelite whose space group is I41/a(88). The two other compounds (A = Li, Na) have a zircon type structure: I41/ amd(141). Unit-cell parameters and powder diffraction data for the three compounds are reported.

A comparison between the results of ab initio structure determination from X-ray powder diffraction data of a new cadmium hydroxide nitrate, Cd5(OH)8 (NO3)2·2H2O (SG C2/m), and those obtained from single crystal data is presented. The powder diffraction pattern has been analysed by an indexing method and fitting techniques. A total of 119 unambiguously indexed reflections has been extracted and used in subsequent treatment. The power of powder techniques to index the pattern and to find the structure model by normal Patterson and Fourier methods is clearly shown. The refinement of approximate coordinates has been carried out by the Rietveld method (444 reflections). The comparison of results with those obtained from single crystal data (2218 reflections) shows that the precision of positional parameter values is lower by a factor of 10, on average, in the powder study. These results are discussed in terms of crystallographic parameters (number of reflections used, number of parameters to refine, contrast between atoms) and, also, in terms of sample dependent properties (preferred orientation effect, impurity). Finally, the crystal structure has been derived from powder data with a precision probably sufficient for most purposes.

Pearson VII functions, some of the most useful descriptions of the intensity distribution within the X-ray powder reflection, have been used to study distortion in the perovskite-type structure of KMnF3. Separate full-widths, Δ, at half-maximum intensity, and Pearson exponents, m, were taken for the low- and high-angle sides of the profiles. The background was assumed to be linear. For the distorted structure, summation was made over all overlapping lines that might possibly contribute to the observed profile. Measurements were performed using a powder diffractometer with a specially adapted electronic system consisting of an automatic data recorder and a method, developed at this laboratory, for transferring data to an IBM PC/AT computer. By these means it could be shown that at 10° K the crystal structure of KMnF3distorts from cubic to monoclinic.

The crystal structure of the tysonite-type superstructure of β-PrF3 has been studied by X-ray powder diffraction and high-energy electron diffraction from single crystals. The crystal data are: a = 7.0795(1) Å, c = 7.2380(2) Å, Z = 6, hexagonal system, space group (No. 165), ρcalc = 6.28 g cm−3. Atomic parameters and interatomic distances are presented from the final refinement with Rconv = 1.72%.