Published in IUCrJ
Single crystals of the m = 8 member of the low-dimensional monophosphate tungsten bronzes (PO2)4(WO3)2 m family were grown by chemical vapour transport technique and the high crystalline quality obtained allowed a reinvestigation of the physical and structural properties. Resistivity measurements revealed three anomalies at T C1 = 258 K, T C2 = 245...
Published in Journal of Structural Chemistry
The work reports different forms of solid solution ordering: from the well-known atom redistribution processes over positions and the decomposition of the solid solution to the formation of superstructures, modulated structures, rotation of atomic groups, splitting of sites. For each ordering form as a crystal chemical phenomenon the position of at...
Published in Acta crystallographica. Section A, Foundations and advances
This paper presents a general algorithm for generating the isotropy subgroups of superspace extensions of crystallographic space groups involving arbitrary superpositions of multi-k order parameters from incommensurate and commensurate k vectors. Several examples are presented in detail in order to illuminate each step of the algorithm. The practic...
High resolution X-ray study reveals the wave vector change in the modulated structure of the quasi-one dimensional compound beta'-Cu vanadium bronze. Structural modulation of the reduced wave vector q0 = (0, 0.305, 0) emerges below 220 K in beta'-Cu0.29V2O5 . For beta'-Cu0.39V2O5, not the single q modulation but two kinds of modulations were observ...
Published in Zeitschrift für Kristallographie - Crystalline Materials
Discontinuous modulation functions called crenel and saw-tooth have been developed for description and refinement of strongly modulated crystal structures with abrupt changes of modulation parameters. Although used for refinement of many modulated structures and mentioned in books on aperiodic crystals, technical details of such refinements have ne...
Published in Zeitschrift für Kristallographie - Crystalline Materials
The solid solutions La2–xPrxO2MnSe2 (0≤x≤1) and La2–xNdxO2MnSe2 (0≤x≤0.6) were synthesized in a NaI/KI flux between 800 and 900°C. The selenide oxides adopt a ZrCuSiAs-related structure with modulated [MnSe2]2–-layers which consist of a mixture of edge- and corner-sharing MnSe4/2-tetrahedra. The crystal structures are described with a (3+1)D model ...
Published in Acta crystallographica Section B, Structural science, crystal engineering and materials
The crystal structure solution of modulated compounds is often very challenging, even using the well established methodology of single-crystal X-ray crystallography. This task becomes even more difficult for materials that cannot be prepared in a single-crystal form, so that only polycrystalline powders are available. This paper illustrates that th...
Published in Acta crystallographica Section B, Structural science, crystal engineering and materials
Electron crystallography has made enormous progress over the last decade. It can provide the necessary information that complements powder diffraction data and allows for successful structure analysis of (not only) modulated structures.
Published in Acta crystallographica. Section A, Foundations of crystallography
It is shown that the Euclidean group of translations, when treated as a Lie group, generates translations not only in Euclidean space but on any space, curved or not. Translations are then not necessarily vectors (straight lines); they can be any curve compatible with the parameterization of the considered space. In particular, attention is drawn t...
Published in Acta crystallographica Section B, Structural science, crystal engineering and materials
A second-order phase transition with both displacive and disorder mechanisms was discovered in Lu4AlCu2B9O23 using single-crystal X-ray diffraction techniques by cooling down the sample to 110 K. Low-temperature structure modulations are mainly associated with Cu atoms surrounded by O atoms. The fivefold asymmetric environment leads to a special co...
