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Structural evolution of a La2Ti2O7 ferroelectric compound possessing perovskite‐type slabs at elevated temperatures was investigated using the single‐crystal X‐ray diffraction technique. The monoclinic low‐temperature phase (L) transformed into the orthorhombic high‐temperature phase (H) via an incommensurately modulated phase (IC) between ∼989 and ∼1080 K. The L–IC transition was considered to be of the first order, with the L+IC two‐phase co‐existing region between ∼989 and ∼1027 K. The structure of IC was determined from the (3+1)‐dimensional superspace representation with a modulation vector q = αao (α ≃ 0.49), where ao is the a‐axis vector of the basic cell. The structural modulation originated from the variation of the tilt angle of the TiO6 octahedra in the perovskite‐type slab in association with small positional displacements of La atoms. The IC–H transition took place at ∼1080 K and was close to the second order. During the IC–H transition, nanoscale flat plate domains having either a cell twin of the L‐type structural modules or a cell twin of the alternating H‐ and L‐type structural modules began to appear in the approximant structure of IC. The thickness of the flat plate domains then grew rapidly along the modulation vector in proportion to (½ − α)−1 as α approached ½ with decreasing temperature. In the two‐phase L+IC co‐existing region, the IC phase consisting of the two types of cell twins was gradually replaced with the low‐temperature monoclinic phase L, which is not cell twinned but rather twinned macroscopically by the L‐type structural modules. Crystals of La2Ti2O7 undergo successive phase transitions between the low‐temperature monoclinic phase and the high‐temperature orthorhombic phase with an intermediate incommensurately modulated phase at around 1000 K. [ABSTRACT FROM AUTHOR]

In situ transmission electron microscopy observation revealed that BaGd2Mn2O7 undergoes several phase transitions upon heating. The orthorhombic Pnnm phase (I) at room temperature was transformed into a tetragonal P42/ mnm (II) at around 420 K via an intermediate phase. On further heating, the other phase (III) nucleated in the phase II matrix at 623 K and grew until covering the whole inspected region by 723 K. Phase III has a 1.5% lattice mismatch along c compared with phase II, and presumably has a monoclinic symmetry. The transition between II and III was of the first order. [ABSTRACT FROM AUTHOR]

In situ transmission electron microscopy observation revealed that BaGd2Mn2O7 undergoes several phase transitions upon heating. The orthorhombic Pnnm phase (I) at room temperature was transformed into a tetragonal P42/ mnm (II) at around 420 K via an intermediate phase. On further heating, the other phase (III) nucleated in the phase II matrix at 623 K and grew until covering the whole inspected region by 723 K. Phase III has a 1.5% lattice mismatch along c compared with phase II, and presumably has a monoclinic symmetry. The transition between II and III was of the first order. [ABSTRACT FROM AUTHOR]

The article presents information on the crystal structure of the compound trigadolinium ruthenium heptaoxide or Gd3RuO7. The structure is composed of infinite single chains of corner-linked [RuO6] octahedra embedded in the [Gd3O] matrix. The octahedra in the P21nb modification have two tilt systems about the a and c axes. The title compound contains six crystallographically independent Gd atoms coordinated by seven O atoms each, with interatomic distances ranging from 2.190 (13) to 2.605 (13) Å.

The compound Al6Ti2O13 (hexaaluminium dititanium tridecaoxide) has been synthesized using an arc-imaging furnace, which-allows fast cooling of melted oxides. The structure consists of infinite double chains of polyhedra running along the c axis. These chains are built up by four kinds of strongly distorted oxygen octahedra randomly occupied by either Ti or Al (point symmetry m or m2m), and by trigonal bipyramids exclusively occupied by Al (point symmetry m2m). [ABSTRACT FROM AUTHOR]

The triclinic superstructure of a small crystal of LiCa2Nb3O10, lithium dicalcium triniobium decaoxide, has been investigated by synchrotron X-ray diffraction. The unit cell is an almost rectangular parallelepiped, although there is a 0.245° offset from orthogonality for β. The structure essentially belongs to a homologous series of Li[Na n−3Ca2Nb nO3 n+1] with n = 3, where the moiety in square brackets has a perovskite-type slab structure. The superstructure has a doubled unit-cell volume with respect to the tetragonal aristotype. The NbO6 octahedra are rotated about axes parallel to [110] by approximately 10°. Adjacent slabs are connected by Li atoms and are geo­metrically related by 42 pseudosymmetry lying parallel to c. There are twice as many sites as Li atoms, providing a variation of population at these Li sites. [ABSTRACT FROM AUTHOR]

Presents a study which measured the structure factors for two compositions of garnets using focused synchrotron X-radiation. Difference electron density maps; Effectivenes in chemical bonding; Relative position of the rara-earth atoms in the periodic table.

Studies the structure of holmium diiron crystal using synchrotron X-rays. Deformation electron density; Accumulation of residual electrons; Spin-coupling mechanism; Indicators of exchange repulsion.

Studies the crystal structure of heptacalcium hexatantalum heptazirconium hexatriacontaoxide using synchrotron radiation data. Space groups of the structure; Refinements using direct methods; Metal-atom ordering scheme; Bond-valence sums.

Reports on the solution and refinement of the structure of heptabismuth tritantalum octadecaoxide, Bi[sub 7]Ta[sub 3]O[sub 18], using single crystal X-ray diffraction data. Description of the metal-atom array; Full ordering of the metal-atom populations and oxygen atoms positions; Successful modeling of the twin component observed during data collection in the refinement.

Reports on the measurement of structure factors for small hydrothermally grown orthorhombic neodymium and dysprosium iron oxides with focused synchrotron radiation using a fast avalanche photodiode counter. Coordination of the magnetic atoms in the structure as reflected in the higher symmetry in the deformation electron density maps.

β-Al2TiO5 (dialuminium titanium penta­oxide), grown by rapid cooling of a melt of equimolar amounts of Al2O3 and TiO2, adopts the same overall structure as that crystallized by more conventional methods, such as sintering. Nevertheless, re­investigation of this structure has resulted in an improved structure model with previously unknown site preferences determined. Ti prefers the slightly more regular 4 c octa­hedral site, leaving more room for Al at the 8 f octa­hedral site. The formula has been determined as [4c][Al0.626 (7)Ti0.374 (7)][8 f][Al0.687 (3)Ti0.313 (3)]2O5. [ABSTRACT FROM AUTHOR]

Flux-grown gadolinium aluminate perovskite, GdAlO3, was examined using single-crystal 0.7 Å-wavelength synchrotron X-ray diffraction. In the context of other well categorized rare earth aluminate (RAlO3) perovskite phases, the orthorhombic Pnma symmetry determined for the current compound is unsurprising. Corner-linked AlO6 octahedra form the structural backbone of RAlO3 perovskites and distort to accommodate the various rare earth ions in the structural voids. For GdA103, the octahedral distortion, characterized by tilting of the octahedra about the shortest R—Al—R vectors, and octahedral deformation, characterized by strain of the octahedra along those axes, are in accordance with trends in the RAlO3 series. [ABSTRACT FROM AUTHOR]

The room-temperature structure of potassium titanyl phosphate (KTiOPO4, KTP) with Pna21 symmetry has been studied by means of synchrotron radiation. Each of the two crystallographically unique K1 and K2 cations is split over two sites that are shifted along the c direction by 0.287 (13) and 0.255 (13) Å for the K1 a/ b and K2 a/ b pairs, respectively. The refined populations of the minor K1 b and K2 b sites are 0.102 (12) and 0.132 (17), respectively. It is shown that accurate high-resolution synchrotron data ( Rmerged = 0.015 for 25 010 reflections, 9456 unique, sinθ/λ limit > 1.0) are required for the determination of a reliable structure model. [ABSTRACT FROM AUTHOR]

The structure of a new orthorhombic trirubidium pentatantalum oxide (Rb3Ta5O14) phase with Pnma symmetry was identified from a half sphere of synchrotron X-ray data measured at a wavelength of 0.85 Å. This notionally linked TaO6 octahedral structure broadly consists of three different modifications of the pyrochlore ring motif with layer stacking normal to (205) planes. Successive pyrochlore layers do not simply stack normal to these planes but are offset along the [100] axis. An unusual aspect of this structure is the occurrence of TaO5 trigonal bipyramids in structurally complex regions where the modified pyrochlore rings connect. [ABSTRACT FROM AUTHOR]

Single crystals of dineodymium(III) dititanium(IV) hepta-oxide, Nd2Ti2O7, were synthesized by the flux method and found to belong to the family of compounds with perovskite-type structural motifs. The asymmetric unit contains four Nd, four Ti and 14 O-atom sites. The perovskite-type slabs are stacked parallel to (010) with a thickness corresponding to four corner-sharing TiO6 octa-hedra. The Nd and Ti ions are displaced from the geometrical centres of respective coordin-ation polyhedra so that the net polarization occurs along the c axis. The investigated crystals were all twinned and have a halved monoclinic unit cell in comparison with the first structure determination of this compound [Scheunemann & Müller-Buschbaum (1975 ▶). J. Inorg. Nucl. Chem. 37, 2261-2263].

Single crystals of the title compound, calcium neodymium ruthenate, (Ca(x)Nd(11-x))Ru(4)O(24) (x = 4.175), have been grown by the flux method. The structure consists of two crystallographically independent RuO(6) octa-hedra, which are isolated from each other and embedded in a matrix composed of the Ca and Nd atoms. There are seven M sites which accommodate the Ca and Nd atoms with different populations. Four M sites at general positions are enriched with Nd, whereas the remaining three M sites on twofold rotation axes are enriched with Ca. The coordination numbers of O atoms to the M sites range from 6 to 9. The mean oxidation state of Ru was estimated at +4.79 from the composition analysis. The title compound is non-centrosymmetric and potentially multiferroic.

Single crystals of the title compound, strontium tetra-praseo-dymium tris-(silicate) oxide, SrPr(4)(SiO(4))(3)O, have been grown by the self-flux method using SrCl(2). The structure is isotypic with the apatite supergroup family having the generic formula (IX)M1(2) (VII)M2(3)((IV)TO(4))(3)X, where M = alkaline earth and rare earth metals, T = Si and X = O. The M1 site (3.. symmetry) is occupied by Pr and Sr atoms with almost even proportions and is surrounded by nine O atoms forming a tricapped trigonal prism. The M2 site (m.. symmetry) is almost exclusively occupied by Pr and surrounded by seven O atoms, forming a distorted penta-gonal bipyramid. The Si atom (m.. symmetry) is surrounded by two O (m.. symmetry) and two O atoms in general positions, forming an isolated SiO(4) tetra-hedron. Another O atom at the inversion centre (.. symmetry) is surrounded by three M2 sites, forming an equilateral triangle perpendicular to the c axis.

The structure of the title compound, Sr-bearing oxonitrido-aluminosilicate (Sr-sialon), contains two types of channels running along the a axis, with the three unique Sr atoms (coordinatioon number seven) residing in the larger one. The channels cross a three-dimensional Si-Al-O-N network, in which the Si and Al atoms are in a tetra-hedral coordination with N and O atoms. The chemical composition of the crystal is close to Sr(3)Al(3)Si(13)N(21)O(2) (tris-trontium trialuminium trideca-silicon henicosa-nitride dioxide), which can be expressed as a mixture of SrSiN(2), Si(3)N(4), AlN, and SiO(2) components in the molar ratio 3:3:3:1. The crystal studied was metrically orthorhombic, consisting of four twin components related by metric merohedry.

The structure of a new orthorhombic trirubidium pentatantalum oxide (Rb(3)Ta(5)O(14)) phase with Pnma symmetry was identified from a half sphere of synchrotron X-ray data measured at a wavelength of 0.85 A. This notionally linked TaO(6) octahedral structure broadly consists of three different modifications of the pyrochlore ring motif with layer stacking normal to (205) planes. Successive pyrochlore layers do not simply stack normal to these planes but are offset along the [100] axis. An unusual aspect of this structure is the occurrence of TaO(5) trigonal bipyramids in structurally complex regions where the modified pyrochlore rings connect.