Electron density distribution and crystal structure of lithium barium silicate, Li2BaSiO4

2010 ◽  
Vol 25 (4) ◽  
pp. 336-341 ◽  
Author(s):  
Tatsunari Kudo ◽  
Yoshinori Hirano ◽  
Koichi Momma ◽  
Koichiro Fukuda
Keyword(s):  
Crystal Structure ◽  
Electron Density ◽  
Structural Model ◽  
Rietveld Method ◽  
Three Dimensional ◽  
Direct Methods ◽  
Atomic Displacement ◽  
Entropy Method ◽  
Reliability Indices ◽  
Atomic Displacement Parameters

Crystal structure of Li2BaSiO4 was reinvestigated by laboratory X-ray powder diffraction. The title compound was hexagonal with space group P63cm, Z=6, unit-cell dimensions a=0.810 408(2) nm, c=1.060 829(4) nm, and V=0.603 370(3) nm3. The initial structural model was successfully derived by the direct methods and further refined by the Rietveld method, with the anisotropic atomic displacement parameters being assigned for all atoms. The reliability indices calculated from the Rietveld refinement were Rwp=6.72%, S=1.17, Rp=5.06%, RB=1.86%, and RF=0.98%. The maximum-entropy method-based pattern fitting (MPF) method was used to confirm the validity of the structural model, in which conventional structure bias caused by assuming intensity partitioning was minimized. The final reliability indices calculated from MPF were Rwp=6.74%, S=1.17, Rp=5.10%, RB=1.49%, and RF=0.69%. Atomic arrangements of the final structural model were in excellent agreement with the three-dimensional electron-density distributions determined by MPF.

Electron density distribution and crystal structure of lithium strontium silicate, Li2SrSiO4

2010 ◽  
Vol 25 (1) ◽  
pp. 4-8 ◽  
Author(s):  
Yoshinori Hirano ◽  
Tomoyuki Iwata ◽  
Koichi Momma ◽  
Koichiro Fukuda
Keyword(s):  
Crystal Structure ◽  
Electron Density ◽  
Structural Model ◽  
Rietveld Method ◽  
Three Dimensional ◽  
Direct Methods ◽  
Entropy Method ◽  
Reliability Indices ◽  
Cell Dimensions ◽  
Unit Cell Dimensions

Crystal structure of Li2SrSiO4 was reinvestigated by laboratory X-ray powder diffraction. The title compound was trigonal with space group P3121, Z=3, unit-cell dimensions a=0.502 281 (4) nm and c=1.245 520(8) nm, and V=0.272 129(3) nm3. The initial structural model was derived by the direct methods and further refined by the Rietveld method. The maximum-entropy method-based pattern fitting (MPF) method was used to confirm the validity of the structural model, in which conventional structure bias caused by assuming intensity partitioning was minimized. The final reliability indices calculated from MPF were Rwp=8.04%, S=1.22, Rp=6.01%, RB=1.50%, and RF=0.66%. Atomic arrangements of the final structural model were in excellent agreement with the three-dimensional electron-density distributions determined by MPF.

Crystal structure of layered perovskite compound, Li2LaTa2O6N

2011 ◽  
Vol 26 (1) ◽  
pp. 4-8 ◽  
Author(s):  
Motoaki Kaga ◽  
Hirokazu Kurachi ◽  
Toru Asaka ◽  
Bing Yue ◽  
Jinhua Ye ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Structural Model ◽  
Rietveld Method ◽  
Direct Methods ◽  
Atomic Displacement ◽  
Layered Perovskite ◽  
Reliability Indices ◽  
Layered Perovskite Structure ◽  
Atomic Displacement Parameters ◽  
Unit Cell Dimensions

The crystal structure of Li2LaTa2O6N was determined from laboratory X-ray powder diffraction data (Cu Kα1) using the Rietveld method. The title compound is tetragonal with space group I4/mmm, Z=2, and unit-cell dimensions a=0.395 049(4) nm, c=1.850 97(3) nm, and V=0.288 869(6) nm3. The initial structural model was successfully derived by the direct methods and further refined by the Rietveld method, with the anisotropic atomic displacement parameters being assigned for all atoms. The final reliability indices were Rwp=5.73%, S=1.46, Rp=4.33%, RB=1.13%, and RF=0.53%. Li2LaTa2O6N has a layered perovskite structure similar to that of Li2LaTa2O7.

Reinvestigation of crystal structure and structural disorder of Ba3MgSi2O8

2009 ◽  
Vol 24 (3) ◽  
pp. 180-184 ◽  
Author(s):  
Tomoyuki Iwata ◽  
Tatsuya Horie ◽  
Koichiro Fukuda
Keyword(s):  
Crystal Structure ◽  
Structural Model ◽  
Rietveld Method ◽  
Structure Refinement ◽  
Three Dimensional ◽  
Structural Disorder ◽  
Entropy Method ◽  
Reliability Indices ◽  
Distribution Maps ◽  
Atom Model

Crystal structure and structural disorder of Ba3MgSi2O8 were reinvestigated by laboratory X-ray powder diffraction. The title compound was found to be trigonal with space group P3m1, Z=1, and unit-cell dimensions a=0.561 453(4) nm, c=0.727 629(4) nm, and V=0.198 641(2) nm3. The initial structural model used for structure refinement was taken from that of glaserite (K3NaS2O8) and modified by a split-atom model. In the split-atom model, one of the two types of Ba sites and that of SiO4 tetrahedra were, respectively, positionally and orientationally disordered. The new crystal structure and structural disorder were refined by the Rietveld method. The maximum-entropy-method-based pattern fitting (MPF) method was used to confirm the validity of the split-atom model, in which conventional structure bias caused by assuming intensity partitioning was minimized. The final reliability indices calculated from MPF were Rwp=6.52%, S=1.36, Rp=4.84%, RB=0.97%, and RF=0.52%. Details of the disorder structure of Ba3MgSi2O8 are shown in the three-dimensional and two-dimensional electron-density distribution maps determined by MPF.

Electron-density distribution and disordered crystal structure of 12H-SiAlON, SiAl5O2N5

2014 ◽  
Vol 29 (4) ◽  
pp. 318-324 ◽  
Author(s):  
Hiroki Banno ◽  
Takaaki Hanai ◽  
Toru Asaka ◽  
Koji Kimoto ◽  
Hiromi Nakano ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Structural Model ◽  
Rietveld Method ◽  
Direct Methods ◽  
Entropy Method ◽  
Space Group ◽  
Reliability Indices ◽  
Cell Dimensions ◽  
Disordered Crystal ◽  
Unit Cell Dimensions

The crystal structure of SiAl5O2N5 was characterized by laboratory X-ray powder diffraction (CuKα1). The title compound is hexagonal with space group P63/mmc (Z = 2). The unit-cell dimensions are a = 0.303153(3) nm, c = 3.28153(3) nm, and V = 0.261178(5)  nm3. The initial structural model was successfully derived by the direct methods and further refined by the Rietveld method. The final structural model showed the positional disordering of two of the four (Si,Al) sites. The maximum-entropy method-based pattern fitting (MPF) method was used to confirm the validity of the split-atom model, in which conventional structure bias caused by assuming intensity partitioning was minimized. The reliability indices calculated from the MPF were Rwp = 5.00%, S (=Rwp/Re) = 1.25, Rp = 3.76%, RB = 1.26%, and RF = 0.90%. The disordered crystal structure was successfully described by overlapping four types of domains with ordered atom arrangements. The distribution of atomic positions in each of the domains can be achieved in the space group P63mc. Two of the four types of domains are related by a pseudo-symmetry inversion, and the two remaining domains also have each other the inversion pseudo-symmetry.

Electron density distribution and crystal structure of Ca1-x/2AlSi(N3-xOx):Eu2+ (x ∼ 0.11)

2011 ◽  
Vol 26 (S1) ◽  
pp. S38-S43 ◽  
Author(s):  
Daisuke Urushihara ◽  
Toru Asaka ◽  
Takashi Takeda ◽  
Naoto Hirosaki ◽  
Koichiro Fukuda
Keyword(s):  
Crystal Structure ◽  
Electron Density ◽  
Structural Model ◽  
Rietveld Method ◽  
Three Dimensional ◽  
X Ray ◽  
Reliability Indices ◽  
Transmission Electron ◽  
Cell Dimensions ◽  
Unit Cell Dimensions

Crystal structure of Ca1-x/2AlSi(N3-xOx):Eu2+ (x ∼ 0.11) has been characterized using an X-ray powder diffractometer and a transmission electron microscope equipped with an energy dispersive X-ray analyzer (EDX) and an electron energy loss spectrometer (EELS). The title compound is orthorhombic with space group Cmc21, Z = 4, unit-cell dimensions a = 0.979780(7) nm, b = 0.565197(4) nm, c = 0.506356(3) nm, and V = 0.280404(3) nm3. The atom ratio Al:Si was determined to be 1:1 by EDX, and the presence of O atoms in the crystal structure was confirmed by EELS. The x-value and the atomic coordinates of the final structural model were determined by the Rietveld method. The maximum-entropy methods-based pattern fitting (MPF) method was used to confirm the validity of the structural model, in which conventional structure bias caused by assuming intensity partitioning was minimized. The reliability indices calculated from MPF are Rwp = 9.18%, S = 1.17, Rp = 6.77%, RB = 1.91%, and RF = 0.86%. Atomic arrangements of the final structural model are in an excellent agreement with the three dimensional electron-density distributions determined by MPF.

Crystal structure of lanthanum oxyorthosilicate, La2SiO5

2006 ◽  
Vol 21 (4) ◽  
pp. 300-303 ◽  
Author(s):  
Koichiro Fukuda ◽  
Tomoyuki Iwata ◽  
Eric Champion
Keyword(s):  
Crystal Structure ◽  
Structural Model ◽  
Rietveld Method ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Monoclinic Space Group ◽  
X Ray ◽  
Reliability Indices ◽  
Volumetric Expansion ◽  
Tricapped Trigonal Prism

The crystal structure of La2SiO5 was refined from laboratory X-ray powder diffraction data (CuKα1) using the Rietveld method. The crystal structure is monoclinic (space group P21∕c,Z=4) with lattice dimensions a=0.93320(2) nm, b=0.75088(1) nm, c=0.70332(1) nm, β=108.679(1)°, and V=0.46687(1) nm3. The final reliability indices were Rwp=7.14%, RP=5.52%, and RB=3.83%. There are two La sites in the structural model, La1 and La2. La1 is ninefold coordinated to oxygen, forming a tricapped trigonal prism with a mean La1-O distance of 0.263 nm. The La2O7 coordination polyhedron is a distorted capped octahedron with a mean La2-O distance of 0.251 nm. The La1O9 polyhedra share faces and the La2O7 polyhedra share edges, forming two sets of sheets that alternate parallel to the (100) plane. These sheets are linked through SiO4 tetrahedra and non-silicon-bonded oxygen atoms to form a three-dimensional structure. This compound is isomorphous with the low-temperature (X1) phases of R2SiO5 (R=Y and Gd). The volumes of RO9 polyhedra steadily increase with increasing ionic radius of R, from Y3+ to Gd3+ to La3+, which causes substantial volumetric expansion of the crystals.

Crystal structure of calcium zirconium diorthophosphate, CaZr(PO4)2

2003 ◽  
Vol 18 (4) ◽  
pp. 296-300 ◽  
Author(s):  
Koichiro Fukuda ◽  
Kazuko Fukutani
Keyword(s):  
Crystal Structure ◽  
Rietveld Method ◽  
Three Dimensional ◽  
Direct Methods ◽  
Dimensional Structure ◽  
Pentagonal Bipyramid ◽  
Powder Diffraction Data ◽  
Orthorhombic Space Group ◽  
X Ray ◽  
Reliability Indices

The crystal structure of CaZr(PO4)2 was determined from conventional X-ray powder diffraction data using direct methods, and it was further refined by the Rietveld method. The structure was orthorhombic (space group P212121, Z=4) with a=1.448 76(4), b=0.672 13(1), c=0.623 47(2) nm, and V=0.607 10(3) nm3. Final reliability indices were Rwp=6.49%, RB=2.43%, and S=1.32. The Ca atom is sevenfold coordinated, and the Ca atom and surrounding oxygen atoms form a distorted capped octahedron with a mean Ca–O distance of 0.243 nm. The ZrO7 coordination polyhedron is a distorted pentagonal bipyramid with a mean Zr–O distance of 0.216 nm. CaO7, ZrO7, and PO4 polyhedra share edges to form infinite chains with the composition [CaO3ZrO3P2O8]12− along the [010]. Individual chains are linked together, forming a two-dimensional sheet parallel to (100). These sheets are stacked in the [100] direction to form a three-dimensional structure.

Redefinition of satimolite

2018 ◽  
Vol 82 (5) ◽  
pp. 1033-1047 ◽  
Author(s):  
Igor V. Pekov ◽  
Natalia V. Zubkova ◽  
Dmitry A. Ksenofontov ◽  
Nikita V. Chukanov ◽  
Vasiliy O. Yapaskurt ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Rietveld Method ◽  
Three Dimensional ◽  
Direct Methods ◽  
Salt Dome ◽  
Unit Cell ◽  
Unit Cell Parameters ◽  
Cell Parameters ◽  
Octahedral Clusters

ABSTRACTThe borate mineral satimolite, which was first described in 1969 and remained poorly-studied until now, has been re-investigated (electron microprobe analysis, single-crystal and powder X-ray diffraction studies, crystal-structure determination, infrared spectroscopy) and redefined based on the novel data obtained for the holotype material from the Satimola salt dome and a recently found sample from the Chelkar salt dome, both in North Caspian Region, Western Kazakhstan. The revised idealized formula of satimolite is KNa2(Al5Mg2)[B12O18(OH)12](OH)6Cl4·4H2O (Z = 3). The mineral is trigonal, space group R$\bar{3}$m, unit-cell parameters are: a = 15.1431(8), c = 14.4558(14) Å and V = 2870.8(4) Å3 (Satimola) and a = 15.1406(4), c = 14.3794(9) Å and V = 2854.7(2) Å3 (Chelkar). The crystal system and unit-cell parameters are quite different from those reported previously. The crystal structure of the sample from Chelkar was solved based on single-crystal data (direct methods, R = 0.0814) and the structure of the holotype from Satimola was refined on a powder sample by the Rietveld method (Rp = 0.0563, Rwp = 0.0761 and Rall = 0.0667). The structure of satimolite is unique for minerals. It contains 12-membered borate rings [B12O18(OH)12] in which BO3 triangles alternate with BO2(OH)2 tetrahedra sharing common vertices, and octahedral clusters [M7O6(OH)18] with M = Al5Mg2 in the ideal case, with sharing of corners between rings and clusters to form a three-dimensional heteropolyhedral framework. Each borate ring is connected with six octahedral clusters: three under the ring and three over the ring. Large ellipsoidal cages in the framework host Na and K cations, Cl anions and H2O molecules.

Observation of orientational disorder in the hexagonal stuffed tridymite Sr0.864Eu0.136Al2O4by the maximum-entropy method

2004 ◽  
Vol 37 (5) ◽  
pp. 698-702 ◽  
Author(s):  
H. Yamada ◽  
W. S. Shi ◽  
C. N. Xu
Keyword(s):  
Maximum Entropy ◽  
Electron Density ◽  
Maximum Entropy Method ◽  
Rietveld Method ◽  
Rietveld Analysis ◽  
Atomic Displacement ◽  
Entropy Method ◽  
Apical Oxygen ◽  
Threefold Axis ◽  
Density Image

The crystal structure of a strontium europium aluminate, Sr0.864Eu0.136Al2O4, with a novel hexagonal form was investigated by a combination of Rietveld analysis and the maximum-entropy method (MEM) with synchrotron X-ray powder diffraction data. The electron density image calculated by the MEM/Rietveld method revealed that the apical oxygen ion in the AlO4tetrahedron has a broad distribution corresponding to an extraordinarily large atomic displacement parameter. This structure could be expressed by a split-atom model, with which the Rietveld refinement gaveRwp= 2.99% andRB= 4.16%. Subsequently, MEM-based pattern fitting (MPF) decreased theRfactors toRwp= 2.81% andRB= 2.34% and the electron density image clearly showed that the apical oxygen ions of the AlO4tetrahedra are split over three sites around a threefold axis involving an elongated distribution of the residual O ions along thecaxis. These results suggest that AlO4tetrahedra in Sr0.864Eu0.136Al2O4are orientationally disordered.

Synthesis, crystal structure, and thermoelectric properties of a new layered carbide (ZrC)3[Al3.56Si0.44]C3

2007 ◽  
Vol 22 (10) ◽  
pp. 2888-2894 ◽  
Author(s):  
Koichiro Fukuda ◽  
Miyuki Hisamura ◽  
Yusuke Kawamoto ◽  
Tomoyuki Iwata
Keyword(s):  
Crystal Structure ◽  
Electrical Conductivity ◽  
Thermoelectric Properties ◽  
Powder Diffraction ◽  
Rietveld Method ◽  
Direct Methods ◽  
Conductivity Measurements ◽  
Maximal Power ◽  
X Ray ◽  
Reliability Indices

A new quaternary layered carbide, (ZrC)3[Al3.56Si0.44]C3, has been synthesized and characterized by x-ray powder diffraction and thermopower and electrical conductivity measurements. The crystal structure was successfully determined using direct methods and further refined by the Rietveld method. The crystal is trigonal (space group R3m*, Z = 3) with lattice dimensions a = 0.331389(7), c = 4.90084(7) nm, and V = 0.46610(1) nm3. The final reliability indices calculated from the Rietveld refinement were Rwp = 9.53% (S = 1.70), Rp = 7.22%, RB = 1.81%, and RF = 0.94%. The crystal structure is composed of the NaCl-type [Zr3C4] slabs separated by the Al4C3-type [Al0.89Si0.11C] layers. This material had thermoelectric properties comparable to the layered carbides (ZrC)2[Al3.56Si0.44]C3 (Zr2[Al3.56Si0.44]C5), (ZrC)2Al3C2, and (ZrC)3Al3C2 in the temperature range of 373–1273 K, with the maximal power-factor value of 6.6 × 10−5 W m−1K−2 at 545 K. The two quaternary carbides have been found to form a homologous series with the general formula of (ZrC)n[Al3.56Si0.44]C3 (n = 2 and 3).

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