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Showing papers on "Orthorhombic crystal system published in 1991"


Journal ArticleDOI
TL;DR: In this paper, the transition to a ferromagnetic long-range ordered state was found at 0.60 K in the orthorhombic β-phase crystal of p-nitrophenyl nitronyl nitroxide.

498 citations


Journal ArticleDOI
TL;DR: An overall survey of the structural and magnetic features of the La2NiO4+ delta system is presented as a result of neutron diffraction experiments in this article, where a tentative phase diagram is proposed.
Abstract: An overall survey of the structural and magnetic features of the La2NiO4+ delta system is presented as a result of neutron diffraction experiments. The stoichiometric compound ( delta =0) presents two structural phase transitions. At T0 approximately=770 K, La2NiO4 transforms from tetragonal (I4/mmm) to orthorhombic (Bmab); at T1 approximately=80 K, from orthorhombic to a new tetragonal (P42/ncm) phase. Associated with this second phase transition a strong microstrain produces anisotropic broadening of Bragg reflections. La2NiO4 is three-dimensional (3D) antiferromagnetically ordered at room temperature (TN=330 K). A weak ferromagnetic component appears below T1. Oxygen excess suppress the 3D magnetic ordering and the structural phase transformations, giving rise to a non-stoichiometric compound with interstitial oxygens. A tentative phase diagram is proposed.

365 citations


Journal ArticleDOI
TL;DR: In this paper, the first direct measurements of unit cell distortions and equation-of-state parameters of the orthorhombic perovskite as functions of composition and simultaneous high pressure and high temperature were obtained.
Abstract: High-pressure, high-temperature properties of MgSiO3, (Fe01Mg09)SiO3, and (Fe02Mg08)SiO3 perovskites have been investigated using a newly developed X ray diffraction technique involving monochromatic synchrotron radiation The first direct measurements of unit cell distortions and equation-of-state parameters of the orthorhombic perovskite as functions of composition and simultaneous high pressure and high temperature were obtained The experiments were conducted under hydrostatic pressure up to 30 GPa, into the stability field of the perovskite The results demonstrate that the perovskite is elastically anisotropic, with the lattice parameter b being 25% less compressible than a and c Under increasing pressures the orthorhombic perovskite is distorted further away from the ideal cubic structure in agreement with theoretical predictions The 298-K isothermal equations of state of the three perovskites are indistinguishable within the uncertainty limits of the experiment The zero-pressure bulk modulus KT0 = 261 (±4) GPa with its pressure derivative KT0′ = 4 is close to that determined in previous static high pressure measurements The thermal expansion obtained from the high P - T experiments are consistent with previous measurements carried out at zero pressure but shows a strong volume dependence The temperature derivative of the isothermal bulk modulus at constant pressure (∂KT/∂T)p is −63(±05)×10−2 GPa/K Analyses of the high-temperature data give a value for the Anderson-Gruneisen parameter δT of 65–75, which is significantly higher than that used in recent lower mantle models

307 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that a significant fraction of titanium in these samples is situated in the framework positions, and the catalytic properties of these well-defined titanium-modified zeolites will be described in more detail in the subsequent parts of this series.

307 citations


Journal ArticleDOI
06 Jun 1991-Nature
TL;DR: In this article, the crystal structures and cohesive energies for close-packed crystals of C_(60) and C_(70) were predicted using a force field developed recently for sp carbon atoms, and confirmed from calculations, that face-centred cubic packing is more stable than hexagonal close-packing (h.c.).
Abstract: Recent breakthroughs in synthesizing large amounts of C_(60), C_(70) and other fullerenes have made possible studies of the struc-tures and properties of fullerene crystals. Using a force field developed recently for sp carbon atoms, we predict here the crystal structures and cohesive energies for close-packed crystals of C_(60) and C_(70). We predict, and confirm from calculations, that for C_(60) face-centred cubic (f.c.c.) packing is more stable than hexagonal close-packing (h.c.p.), by 0.90 kcal mol−1, whereas for C70 h.c.p. is more stable than f.c.c. by 0.35 kcal mol^(−1). The cubic structure of C60 undergoes an orthorhombic distortion to space group Cmca at 0 K. At higher temperatures there is rapid reorientation (but not free rotation) of C_(60) molecules, suggesting that above about 200 K a phase transition occurs to an orientationally disordered, f.c.c. structure (with a room-temperature lattice parameter of 14.13 A). This may correspond to the first-order transition observed at 249 K. The threefold axes of the C_(60) molecules in the low-temperature structure are not aligned with the threefold crystallographic axes.

291 citations


Journal ArticleDOI
TL;DR: In this article, a homologous series of high pressure phases, Srn−1Cun+1O2n (n = 3, 5, …), were found in the SrOCuO system treated at 6 GPa and 1373-1573 K. These crystallize in orthorhombic structures of space group Cmmm with unit-cell parameters of a ∼ 3.9 A.

232 citations


Journal ArticleDOI
TL;DR: The 3D X-ray structure of human α-lactalbumin, an important component of milk, has been determined at 1·7 A (0·17 nm) resolution by the method of molecular replacement as mentioned in this paper.

190 citations


Journal ArticleDOI
TL;DR: In this article, the tensor properties of the obtained crystals were analyzed from the viewpoint of crystal symmetry, and the ferroelectric domain structure was distinguished in all types of crystals.

167 citations


Journal ArticleDOI
TL;DR: In this article, the Rodrigues vector space is used for the description of orientation data for cubic, hexagonal, tetragonal and orthorhombic crystals, and a method for selecting a unique representative out of the numerous symmetrically equivalent Rodrigues vectors is given.
Abstract: A convenient method for the description of orientation data for cubic, hexagonal, tetragonal and orthorhombic crystals is given. The method can also be used for the representation of disorientation data, where disorientations between any two crystals of the specified symmetry lattices are considered. It is based on the quaternion formalism introduced into the discussion of orientations and disorientations by Grimmer [Acta Cryst. (1974), A30, 685–688], Frank [(1987). Proc. Int. Conf. on Texture of Materials 8 (INCOTOM 8), Santa Fe, USA, pp. 3–13] and others. Since orientations and disorientations can be interpreted as rotations which in turn can be represented by only three parameters a vector description is used. These vectors span a rotation space corresponding to the usual space of Eulerian angles. It is called Rodrigues vector space [Rodrigues (1840). J. Math. Pure Appl. 5, 380–440; Becker & Panchanadeeswaran (1989). Text. Microstruct. 10, 167]. The direction of a Rodrigues vector is parallel to the rotation axis and its length is tan (θ/2), where θ describes the rotation angle. A method for selecting a unique representative out of the numerous symmetrically equivalent Rodrigues vectors is given. Since these selection rules depend on the symmetry of the crystal lattices considered they yield compact domains in the Rodrigues vector space which are typical for each type of lattice or lattice pair. These domains are always bounded by planes. Frank (1987) called them fundamental zones and described them for the orientations of cubic, hexagonal and orthorhombic crystals.

136 citations


Journal ArticleDOI
TL;DR: Sous pression hydrostatique, le GaAs-I cubique subit des transitions de phase vers au moins deux structures orthorhombiques est etudiee par des mesures de transmittance optique, diffusion Raman et absorption des rayons X.
Abstract: Under hydrostatic pressure, cubic GaAs-I undergoes phase transitions to at least two orthorhombic structures. The initial phase transition to GaAs-II has been investigated by optical-transmittance measurements, Raman scattering, and x-ray absorption. The structure of pressurized samples, which are retrieved at ambient, has been studied by x-ray diffraction and high-resolution diffraction microscopy. Various criteria that define the domain of stability of GaAs-I are examined, such as the occurrence of crystalline defects, the local variation in atomic coordination number, or the actual change in crystal structure. These are shown not to occur at the same pressure at 300 K, the latter being observable only several GPa above the actual thermodynamic instability pressure of GaAs-I. Comparison of the evolution of these parameters on increasing and decreasing pressure locates the thermodynamic transition region GaAs-I\ensuremath{\rightarrow}GaAs-II at 12\ifmmode\pm\else\textpm\fi{}1.5 GPa and at 300 K that is lower than generally reported. The use of thermodynamic relations around the triple point, and of regularities in the properties of isoelectronic and isostructural III-V compounds, yields a phase diagram for GaAs which is consistent with this value.

135 citations


Journal ArticleDOI
TL;DR: In this paper, the electrochemical oxidation of La 2 CuO 4 in alkaline solution (1N KOH) has been used for preparing the superconducting phase La 2CuO 4+δ (δ⋍ 0.07).
Abstract: The electrochemical oxidation of La 2 CuO 4 in alkaline solution (1N KOH) has been used for preparing the superconducting phase La 2 CuO 4+δ (δ⋍0.07). Crystallographic data show an enhanced orthorhombic distortion and an increase of the unit cell volume. The transport properties reveal a sharp transition from a metallic behaviour to a superconducting state below 44 K which is corroborated by the noteworthy magnetic properties.

Journal ArticleDOI
TL;DR: In this paper, an industrial laminate, Phenolic CE, is shown to possess seismic anisotropy, which is characteristic of orthorhombic symmetry, i.e., that the material has three mutually orthogonal axes of two-fold symmetry.
Abstract: An industrial laminate, Phenolic CE, is shown to possess seismic anisotropy. This material is composed of laminated sheets of canvas fabric, with an approximately orthogonal weave of fibers, bonded with phenolic resin. It is currently being used in scaled physical modeling studies of anisotropic media at The University of Calgary. Ultrasonic transmission experiments using this material show a directional variation of compressional- and shear-wave velocities and distinct shear-wave birefringence, or splitting. Analysis of group-velocity measurements taken for specific directions of propagation through the material demonstrates that the observed anisotropy is characteristic of orthorhombic symmetry, i.e., that the material has three mutually orthogonal axes of two-fold symmetry. For P waves, the observed anisotropy in symmetry planes varies from 6.3 to 22.4 percent, while for S waves it is observed to vary from 3.5 to 9.6 percent.From the Kelvin-Christoffel equations, which yield phase velocities given a set of stiffness values, expressions are elaborated that yield the stiffnesses of a material given a specified set of group-velocity observations, at least three of which must be for off-symmetry directions.

ComponentDOI
TL;DR: The crystal structure of the DNA decamer C-G-A-T-C-G, G-C and G-A has been solved to a resolution of 1.5 A, with a final R-factor of 16.1% for 5,107 two-sigma reflections as discussed by the authors.

Journal ArticleDOI
TL;DR: In this paper, high-pressure orthorhombic (GdFeO3-type) perovskite polymorphs of MnSnO3 and FeTiO3 have been observed using in situ powder X-ray diffraction in a diamond-anvil cell with synchrotron radiation.
Abstract: New high-pressure orthorhombic (GdFeO3-type) perovskite polymorphs of MnSnO3 and FeTiO3 have been observed using in situ powder X-ray diffraction in a diamond-anvil cell with synchrotron radiation. The materials are produced by the compression of the lithium niobate polymorphs of MnSnO3 and FeTiO3 at room temperature. The lithium niobate to perovskite transition occurs reversibly at 7 GPa in MnSnO3, with a volume change of -1.5%, and at 16 GPa in FeTiO3, with a volume change of -2.8%. Both transitions show hysteresis at room temperature. For MnSnO3 perovskite at 7.35 (8) GPa, the orthorhombic cell parameters are a=5.301 (2) A, b=5.445 (2) A, c=7.690 (8) A and V= 221.99 (15) A3. Volume compression data were collected between 7 and 20 GPa. The bulk modulus calculated from the compression data is 257 (18) GPa in this pressure region. For FeTiO3 perovskite at 18.0 (5) GPa, cell parameters are a=5.022 (6) A, b=5.169 (5) A, c=7.239 (9) A and V= 187.94 (36) A3. Based on published data on the quench phases, the FeTiO3 perovskite breaks down to a rocksalt + baddelyite mixture of “FeO” and TiO2 at 23 GPa. This is the first experimental verification of the pressure-induced breakdown of a perovskite to simple oxides.

Journal ArticleDOI
TL;DR: In this article, the X-ray crystal structures of three basic zinc carboxylate complexes, [Zn4O(O2CR)6] where RC(CH3)3 (pivalate) or C6H5 (benzoate), were reported.

Journal ArticleDOI
TL;DR: The crystal and molecular structures of VH amylose were determined by a constrained linked-atom least-squares refinement, utilizing intensities measured from electron diffraction patterns and stereochemical restraints, and differs somewhat from previous reports which invoked orthorhombic lattices.

Journal ArticleDOI
TL;DR: The phase relation in the system, (La1−xAx)1−yMnO3+z (A=Sr and Ca), has been investigated by XRD method as discussed by the authors, which showed the A site deficiency in ABO3 perovskite structure, and the range, y, was less than 0.1 when x=0, which decreased with increasing alkaline earth content, x.

Journal ArticleDOI
TL;DR: In this paper, a tetrahedral anvil was used to grow monoclinic molybdenum trioxide (MoO3-II) with unit cell parameters.

Journal ArticleDOI
TL;DR: In this paper, the point group of the Ω phase in an Al-4.0 Cu-0.5 Mg- 0.5 Ag (wt%) alloy was determined using CBED and it was shown that the tetragonal structure of the phase is not hexagonal, monoclinic, or orthorhombic as proposed by others.
Abstract: Convergent-beam electron diffraction (CBED) was employed to determine the point group of the Ω phase in an Al-4.0 Cu-0.5 Mg-0.5 Ag (wt%) alloy. The [100]Ω|〈112〉α CBED pattern had 4 mm symmetry and not 2 mm as expected for the orthorhombic Ω structure. The CBED symmetries along the [010]Ω|〈110〉α and [001]Ω|〈111〉α zone axes were 2 mm and the only point group consistent with these symmetries is 4/mmm. Thus, the crystal structure of the Ω phase is not hexagonal, monoclinic, or orthorhombic as proposed by others, but tetragonal. Electron diffraction patterns of the Ω phase can be indexed on the basis of a tetragonal unit-cell with parameters a = b = 0.6066 nm, c = 0.496 nm. In comparison, the equilibrium θ (Al2Cu) phase in AlCu alloys has a tetragonal structure with unit-cell parameters a = b = 0.6066 nm, c = 0.4874 nm. The 1.76% increase in the c-parameter is sufficient for the tetragonal phase (designated θM) to attain nearly perfect atomic matching on the {111}α planes and still maintain 4-fold symmetry along the [001]θM|〈112〉α direction. In addition, the number of variants, hexagonal morphology and preferred growth of the θM phase along 〈112〉α are consistent with symmetry considerations, the proposed θM crystal structure and experiment TEM observations.

Journal ArticleDOI
TL;DR: In this article, mixed perovskites of high quality have been grown from multicomponent melts using the Czochralski method using a mixture of rare-earth aluminium lattices as host lattices.

Journal ArticleDOI
TL;DR: A new polymorph of lithium vanadyl(IV) orthophosphate, β-LiVOPO4, has been synthesized hydrothermally in a sealed quartz glass tube under autogeneous pressure by slowly cooling from 450°C a mixture of Li2O, VO2, and 725 M H3PO4.

Journal ArticleDOI
TL;DR: In this paper, a high-temperature X-ray diffraction study of BaZrO3 perovskites has been carried out to 1200° C. The diffraction patterns are analyzed with Rietveld method so as to refine the unit cell dimensions.
Abstract: High-temperature X-ray diffraction studies of SrZrO3 and BaZrO3 perovskites have been carried out to 1200° C. The diffraction patterns are analyzed with Rietveld method so as to refine the unit cell dimensions. The volumetric thermal expansion coefficient are observed to be 2.98*10-5K-1 for orthorhombic Pbnm phase, 3.24*10-5K-1 for orthorhombic Cmcm phase, 3.75*10-5K-1 for tetragonal I4/mcm phase of SrZrO3 perovskite, and 2.06*10-5K-1 for cubic Pm3m phase of BaZrO3 perovskite, respectively. The linear thermal expansion coefficients of SrZrO3 perovskite show considerable anisotropy of α a >α c >α b for orthorhombic Pbnm phase, which reflect the decrease of distortion of the perovskite. It is demonstrated that thermal expansion of the centrosymmetrically distorted ABX3 perovskite can be empirically expressed as a combination of the changes of [B-X] bond length and tilting angle of BX6 octahedral framework. The octahedral tilting is considered to be the primary order parameter for the ferroelastic type of structural phase transitions in perovskite. Thermodynamically, the tilting induced volume change denotes the “excess volume” and the corresponding thermal expansion represents the “excess thermal expansion” for the lower symmetry phase with respect to its prototype of the cubic perovskite.

Journal ArticleDOI
TL;DR: In this paper, the phase diagram of the tritantalum pentanitride (Ta3N) system has been mapped and its structure has been refined from time-of-flight neutron diffraction data.
Abstract: Polycrystalline tritantalum pentanitride (Ta3Ns) has been prepared from the reaction of TaC15 with ammonia, and its structure has been refined from time-of-flight neutron diffraction data. M,. = 612-88, orthorhombic, Cmcm, a = 3.8862 (1), b = 10.2118 (2), c = 10.2624 (3) A, V = 407.26 (3) A, 3, Z = 4, D,. = 9.99 g cm-3, neutron time-of-flight, Rietveld refinement, wRp, Rp, reduced X 2= 0.061, 0.043, 4.21 for data collected at 16 K. Ta3N5 crystal- lizes with the pseudobrookite (Fe2TiOs) structure. Irregular TaN6 octahedra share edges and corners. Introduction. Several authors have mapped out the phase diagram of the Ta-N system (Brauer & Zapp, 1954; Sch6nberg, 1954b). y-Ta2N crystallizes with close-packed metal atoms; the N atoms fill the octa- hedral sites, e-TaN has the B35 structure type which consists of very densely packed metal atoms; N atoms fill deformed octahedral holes (Brauer & Zapp, 1953; Christensen & Lebech, 1978). Ta4N5 and TasN6 can be prepared as thin films and have been analyzed by electron diffraction (Terao, 1971). At elevated temperatures, 6'-TaNx forms with the rock- salt structure (Gatterer, Dufek, Ettmayer & Kieffer, 1975). Thin films of 6-TaNo.8_09 are reported with the hexagonal WC structure (Brauer & Mohr- Rosenbaum, 1971). Some of these interstitial nitrides

Journal ArticleDOI
TL;DR: In this paper, the crystal structure of antiferroelectric Pb(Yb1/2Nb 1/2)O3 has been characterized using X-ray diffraction and transmission electron diffraction.
Abstract: The crystal structure of antiferroelectric Pb(Yb1/2Nb1/2)O3 has been characterized. Both X-ray diffraction and transmission electron diffraction show two sets of superlattice reflections originating respectively from the B-site atom ordering and the antiparallel lead-atom displacements which suffer within the orthorhombic ao-bo plane along the ao direction. The room-temperature crystal symmetry is considered to be orthorhombic with space group Pbnm (D2h16) and lattice parameters ao=5.918 AA, bo=23.453 AA and co=8.221 AA. High-resolution electron microscopy confirms the diffraction results. A structural phase transition from the lower-symmetry phase to the cubic paraelectric phase occurs at about 302 degrees C on heating.

Journal ArticleDOI
TL;DR: In this article, an analysis of the orientation relation, habit plane and plate patterns are consistent with the concept of a strain-type transition, even though long range diffusion is required.
Abstract: Alloys of composition Ti2AlNb and Ti4AlNb3, cooled from 1400°C and equilibrated at 700°C for 26 days, were both found to consist of two phases: the Ti- and Nb-rich b.c.c. phase and the orthorhombic phase based on Ti2AlNb. Depending on the alloy composition, each phase was observed as a precipitate with a plate morphology in the matrix of the other phase. In both cases the phases share a common direction, [011]b.c.c. | [001]ort, and interface (habit) plane, ( 2 1 1 )b.c.c. | ( 1 1 0 )ort. Geometrical patterns of plates of the different orientational variants were also observed. Analysis of the orientation relation, habit plane and plate patterns are consistent with the concept of a strain-type transition even though long range diffusion is required.

Journal ArticleDOI
TL;DR: In this article, a phase diagram is established which displays the following physical and structural properties of the LaTiO x compounds: a structural phase boundary atx=3.20 separates a new series of 2D layered structures from the 3D orthorhombic one, and a phase boundary exists between a metallic and a weak ferromagnetic state where the magnetic transition temperature can be sensitively tuned by the oxygen stoichiometry.
Abstract: LaTiO x compounds are structurally related to perovskites and there are two known phases. The first,x=3.50, is a 2D layered-type ferroelectric. The second,x=3.00, is a weak ferromagnet with a 3D orthorhombic distorted perovskite structure. 20 samples with varying oxygen stoichiometry between these end members were prepared by floating zone melting, and then characterized by means of X-ray powder diffraction, electron microscopy, thermogravimetric analysis, resistivity and magnetic measurement. A phase diagram is established which displays the following physical and structural properties. A structural phase boundary atx=3.20 separates a new series of 2D layered structures from the 3D orthorhombic one. The former series represents the first conducting titanium oxides with a 2D layered structure to be reported. Atx=3.10 a phase boundary exists between a metallic and a weak ferromagnetic state where the magnetic transition temperatureT c can be sensitively tuned by the oxygen stoichiometryx. Samples withT c between 100 K and 130 K exhibit a metal-semiconductor transition whereas samples with higherT c , up to 149 K, are semiconductors between room temperature and 4.2 K.

Journal ArticleDOI
TL;DR: In this paper, the volume per formula unit in the orthorhombic phase is 10% smaller than in the high-pressure form of Fe2O3 and it is suggested that the volume change is due to a combination of a valence change and a high-spin/low-spin transition.
Abstract: High-pressure X-ray powder diffraction has been performed on corundum-type αFe2O3 (hematite) in the pressure range up to 65 GPa using synchrotron radiation and a diamond anvil cell. A structural phase transformation has been observed with a transition pressure of about 55 GPa. The high-pressure form of Fe2O3 is orthorhombic. The lattice parameters at 60 GPa are a = 4.59(3) A, b = 4.97(3) A, c = 6.68(5) A, Z = 4. The crystal structure is most probably a GdFeO3-type perovskite with space group Pbnm. The volume per formula unit in the orthorhombic phase is 10% smaller than in αFe2O3. It is suggested that the volume change is due to a combination of a valence change and a high-spin/low-spin transition. The bulk modulus, B0, and its pressure derivative, B'0, evaluated at zero pressure for αFe2O3 are B0 = 230(5) GPa and B'0 = 3.5(6).

Journal ArticleDOI
TL;DR: The crystal structures of polymorph II of diisothiocyanatobis(2,2′-bipyridine)iron(II), [Fe(bpy)2(NCS)2], in the high- (298 K) and low-spin states (175, 110 K) were determined by an X-ray diffraction method.
Abstract: The crystal structures of polymorph II of diisothiocyanatobis(2,2′-bipyridine)iron(II), [Fe(bpy)2(NCS)2], in the high- (298 K) and low-spin states (175, 110 K) were determined by an X-ray diffraction method. The crystal is orthorhombic, space group Pcnb and Z=4 over the entire temperature range. At 298 K, a=13.2044 (6), b=16.4820 (7), c=10.1086 (7) A, U=2200.0 (2) A3, Dc=1.462 g cm−3 and at 110 K, a=12.9842 (9), b=16.1067 (12), c=9.8938 (8) A, U=2069.1 (3) A3, Dc=1.555 g cm−3. The structures were refined to R=0.047, 0.044, and 0.042 at 298, 175, and 110 K, respectively. The difference in the average Fe–N bond lengths between high- and low-spin states is 0.17 A. The pressure dependence of the absorption spectra was also measured up to 8.5 GPa using a diamond anvil cell. These results indicate that with increasing pressure the high-spin state at 1 atm starts to change to the low-spin state at 0.3 GPa and that its low-spin state reverts again to the high-spin state at around 3.3 GPa.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the evolution of the distortion of several oxide perovskites with increasing pressure, using EXAFS in the diamond anvil cell, and interpreted the distortion to the ratio f of the volumes of the AO12 dodecahedron and the BO6 octahedron, and to the compressibilities of the polyhedra.
Abstract: We have investigated the evolution of the distortion of several oxide perovskites with increasing pressure, using EXAFS in the diamond anvil cell. Cubic perovskite BaZrO3 remains cubic up to 52 GPa. Orthorhombic perovskite CaGeO3 becomes less distorted as pressure increases, becomes tetragonal at about 12 GPa and evolves toward cubic structure, still not obtained at 23 GPa. The distortion of orthorhombic perovskite SrZrO3 first increases with pressure up to 8 GPa, then decreases until the perovskite becomes cubic at 25 GPa. The results are interpreted in terms of a systematics, relating the distortion to the ratio f of the volumes of the AO12 dodecahedron and the BO6 octahedron, and to the compressibilities of the polyhedra. For cubic perovskites, f=5, which may correspond to a situation where the compressibilities of octahedra and dodecahedra are equal.

Journal ArticleDOI
01 Sep 1991-Zeolites
TL;DR: In this article, the structure of [Zr]-ZSM-5 with orthorhombic symmetry was analyzed using XRD and selected area electron diffraction, and it was shown that the symmetry change could be prevented by carrying out the calcination carefully, first in N2 and then in air.