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Deals with a study which investigated the spin-Peierls transition in a copper compound using x-ray diffraction techniques. Methods; Results; Discussion.

Quantum spins placed on the corners of a square lattice can dimerize and form singlets, which then can be transformed into a magnetic state as the interactions between dimers increase beyond thresh-old. This is a strictly 2D transition in theory, but real-world materials often need the third dimension to stabilize long-range order. We use high pressures to convert sheets of Cu2+ spin 1/2 dimers from local singlets to global antiferromagnet in the model system SrCu2(BO3)2. Single-crystal neutron diffraction measurements at pressures above 5 GPa provide a direct signature of the antiferromagnetic ordered state, whereas high-resolution neutron powder and X-ray diffraction at commensurate pressures reveal a tilting of the Cu spins out of the plane with a critical exponent characteristic of 3D transitions. The addition of anisotropic, interplane, spin-orbit terms in the venerable Shastry-Sutherland Hamiltonian accounts for the influence of the third dimension. [ABSTRACT FROM AUTHOR]

Polycrystalline zircon-type dysprosium orthovanadate, DyVO4, prepared from a single crystal grown by slow cooling from PbO/PbF2 flux, was studied by X-ray diffraction. Rietveld refinement provided the following unit cell size and oxygen atom coordinates: a = 7.14811(4) Å; c = 6:30825(4) Å, V = 322.323(3) Å3, y(O2-) = 0.4300(4); z(O2-) = 0.2082(4) which are of a particularly high accuracy and show consistency with earlier reported values. Density functional theory calculations within the generalized gradient approximation for the exchange-correlation energy were also performed, providing values of structure parameters which differ by less than 2% from the experimental ones. The agreement between theory and experiment demonstrates the value of these calculations for understanding the structure of compounds of RVO4 family. In addition, density functional theory calculations were performed for the scheelite-type DyVO4; also for this polymorph the discrepancy with the only known set of lattice parameters is less than 2%. Values of oxygen atom coordinates have not been reported yet for this polymorph; here, the calculated ones are quoted. [ABSTRACT FROM AUTHOR]

High-pressure energy-dispersive X-ray diffraction study were performed on zircon-type phase of terbium orthovanadate, TbVO4, in the pressure range up to 7 GPa. For analysis of the collected diffraction spectra, Le Bail refinements were performed. The values of bulk modulus and its pressure derivative (B′ = 121 GPa, B′ = 4:1) were obtained from fitting of the second-order Birch-Murnaghan equation of state. The equation of state derived for TbVO4, is compared with earlier data based on the Raman spectroscopic studies and with data of several other rare-earth orthovanadates. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented in response to the article "Interplay of magnetism and structure in the Shastry--Sutherland model," by M. E. Zayed and colleagues, that was published in the previous issue.

Abstract: Spatially resolved X-ray diffraction techniques provide useful quantitative information on the defect structure distribution for single crystals, thin films or nanowires. In this study, high-resolution X-ray diffraction is used at a laboratory X-ray source, to study the defect structure of undoped and Yb doped needle-shaped PrVO4 crystals grown by the slow cooling method, and to observe the effect of Yb doping on crystal structure and quality. General information on the defect structure is derived from reciprocal lattice-point maps at several selected points. Details of the defect structure are obtained with the use of mapping of triple axis rocking curves and of 2θ/ω diffraction curves. Combining these techniques provided useful information on the variation of defect nature and distribution along the crystals. There is no particular difference between the undoped and doped crystals. They are typically single crystalline, some of them are built from several blocks with misorientation angles up to several hundred arcsec. The full width at half maximum (FWHM) at the central part of the crystals is as low as about 10–12arcsec. There is a tendency of FWHM to increase close to the crystal tips, demonstrating that the crystals are of lower crystalline quality at these regions. The mappings performed for (100) and (010) faces show that one of faces exhibits a small curvature (the lattice tilt being smaller than 2arcsec/mm), whereas the other is characterized by a larger curvature (the tilt by at least three times larger). Unexpectedly, the reciprocal lattice-point maps for (100) and (010) crystal faces include an additional reciprocal lattice point of weak intensity. Its possible origin is discussed. [Copyright &y& Elsevier]

Polycrystalline zircon-type dysprosium orthovanadate, DyVO4, prepared from a single crystal grown by slow cooling from PbO/PbF2 flux, was studied by X-ray diffraction. Rietveld refinement provided the following unit cell size and oxygen atom coordinates: a = 7.14811(4) Å; c = 6:30825(4) Å, V = 322.323(3) Å3, y(O2-) = 0.4300(4); z(O2-) = 0.2082(4) which are of a particularly high accuracy and show consistency with earlier reported values. Density functional theory calculations within the generalized gradient approximation for the exchange-correlation energy were also performed, providing values of structure parameters which differ by less than 2% from the experimental ones. The agreement between theory and experiment demonstrates the value of these calculations for understanding the structure of compounds of RVO4 family. In addition, density functional theory calculations were performed for the scheelite-type DyVO4; also for this polymorph the discrepancy with the only known set of lattice parameters is less than 2%. Values of oxygen atom coordinates have not been reported yet for this polymorph; here, the calculated ones are quoted. [ABSTRACT FROM AUTHOR]

High-pressure energy-dispersive X-ray diffraction study were performed on zircon-type phase of terbium orthovanadate, TbVO4, in the pressure range up to 7 GPa. For analysis of the collected diffraction spectra, Le Bail refinements were performed. The values of bulk modulus and its pressure derivative (B′ = 121 GPa, B′ = 4:1) were obtained from fitting of the second-order Birch-Murnaghan equation of state. The equation of state derived for TbVO4, is compared with earlier data based on the Raman spectroscopic studies and with data of several other rare-earth orthovanadates. [ABSTRACT FROM AUTHOR]