Showing papers on "Tetragonal crystal system published in 2002"
TL;DR: In this paper, the phase transition from the high-temperature prototypic cubic structure to one of tetragonal (673-773) and then rhombohedral structures (5-528) has been established.
Abstract: Rietveld neutron powder profile analysis of the compound Na0.5Bi0.5TiO3 (NBT) is reported over the temperature range 5–873 K. The sequence of phase transitions from the high-temperature prototypic cubic structure (above 813 K), to one of tetragonal (673–773 K) and then rhombohedral structures (5–528 K) has been established. Coexisting tetragonal/cubic (773–813 K) and rhombohedral/tetragonal (with an upper temperature limit of 145 K between 528 and 673 K) phases have also been observed. Refinements have revealed that the rhombohedral phase, space group R3c, with aH = 5.4887 (2), cH = 13.5048 (8) A, V = 352.33 (3) A3, Z = 6 and Dx = 5.99 Mg m−3, exhibits an antiphase, a−a−a− oxygen tilt system, ω = 8.24 (4)°, with parallel cation displacements at room temperature. The tetragonal phase, space group P4bm, with aT = 5.5179 (2), cT = 3.9073 (2) A, V = 118.96 (1) A3, Z = 2 and Dx = 5.91 Mg m−3, possesses an unusual combination of in-phase, a0a0c+ oxygen octahedra tilts, ω = 3.06 (2)°, and antiparallel cation displacements along the polar axis. General trends of cation displacements and the various deviations of the octahedral network from the prototypic cubic perovskite structure have been established and their systematic behaviour with temperature is reported. An investigation of phase transition behaviour using second harmonic generation (SHG) to establish the centrosymmetric or non-centrosymmetric nature of the various phases is also reported.
799 citations
TL;DR: In this paper, the stability and evolution of ferroelectric domain structures in thin films are studied and Elastic solutions are derived for both elastically anisotropic and isotropic thin films with arbitrary domain structures, subject to mixed stress-free and constraint boundary conditions.
446 citations
TL;DR: The cubic-tetragonal phase transition of CH 3 NH 3 PbI 3 was investigated by single crystal X-ray diffractometry as discussed by the authors, where the crystal structure was refined at five temperatures in the teragonal phase.
Abstract: The cubic–tetragonal phase transition of CH 3 NH 3 PbI 3 was investigated by single crystal X-ray diffractometry. The crystal structure was refined at five temperatures in the teragonal phase. The PbI 6 octahedron rorates around the c -axis alternatively to construct the SrTiO 3 -type tetragonal structure. A methylammonium ion is partially orderd; 24 disordered states in the cubic phase are reduced to 8. With decreasing temperature, the rotation angle of the octahedron increases monotonically, which indicates it is an order parameter of the cubic-tetragonal transition.
438 citations
TL;DR: In this paper, the microscopic mechanism leading to the stabilization of cubic and tetragonal forms of zirconia (ZrO2) is analyzed by means of a self-consistent tight-binding model.
322 citations
TL;DR: In this article, the synthesis and characterization of the first perovskite nanotubes made by sol−gel template synthesis is demonstrated, and the structures formed are 200-nm outer diameter tubes with 50-μm lengths.
Abstract: In this communication, the synthesis and characterization of the first perovskite nanotubes made by sol−gel template synthesis is demonstrated. SEM shows that the structures formed are 200-nm outer diameter tubes with 50-μm lengths. TEM and electron diffraction reveal that the tubes are polycrystalline. In a comparison of the d-spacing between electron and bulk powder X-ray diffraction patterns, the crystalline phase of the nanotubes were assigned cubic for barium titatnate (BaTiO3) and tetragonal for lead titanate (PbTiO3).
266 citations
TL;DR: In this paper, the spontaneous polarization of epitaxial BaTiO$_3$/SrTiO $3$ superlattices was studied as a function of composition using first-principles density functional theory within the local density approximation.
Abstract: The spontaneous polarization of epitaxial BaTiO$_3$/SrTiO$_3$ superlattices is studied as a function of composition using first-principles density functional theory within the local density approximation. With the in-plane lattice parameter fixed to that of bulk SrTiO$_3$, the computed superlattice polarization is enhanced above that of bulk BaTiO$_3$ for superlattices with BaTiO$_3$ fraction larger than 40%. In contrast to their bulk paraelectric character, the SrTiO$_3$ layers are found to be {\it tetragonal and polar}, possessing nearly the same polarization as the BaTiO$_3$ layers. General electrostatic arguments elucidate the origin of the polarization in the SrTiO$_3$ layers, with important implications for other ferroelectric nanostructures.
245 citations
TL;DR: In this paper, a tetragonal lattice suitable for a large photonic band gap (PBG) can be synthesized by a regular array of square spiral structures grown from a simple, prepatterned substrate using physical vapor deposition and advanced substrate motion.
Abstract: We present a simple, versatile technique for the fabrication of large, three-dimensional gap photonic crystals using glancing angle deposition (GLAD). A tetragonal lattice suitable for a large photonic band gap (PBG) can be synthesized by a regular array of square spiral structures grown from a simple, prepatterned substrate using physical vapor deposition and advanced substrate motion. Tetragonal square spiral crystals with a predicted PBG of up to 15% for a silicon structure can be produced in the visible, NIR, and IR spectrum. These PBG's exhibit good stability for large areas of parameter space that can be readily mapped out by the GLAD process through the variation of deposition parameters.
229 citations
TL;DR: In this article, the authors investigated the behavior of bcc Mo and Nb under large strain using the ab initio pseudopotential density-functional method, and calculated the ideal shear strength of the {l_brace}211{r_brace] slip systems and the ideal tensile strength in the direction, which are believed to provide the minimum shear and tensile strengths.
Abstract: The behavior of bcc Mo and Nb under large strain was investigated using the ab initio pseudopotential density-functional method. We calculated the ideal shear strength of the {l_brace}211{r_brace} slip systems and the ideal tensile strength in the direction, which are believed to provide the minimum shear and tensile strengths. As either material is sheared in either of the two systems, it evolves toward a stress-free tetragonal structure that defines a saddle point in the strain-energy surface. The inflection point on the path to this tetragonal ''saddle-point'' structure sets the ideal shear strength. When either material is strained in tension along , it initially follows the tetragonal, ''Bain,'' path toward a stress-free fcc structure. However, before the strained crystal reaches fcc, its symmetry changes from tetragonal to orthorhombic; on continued strain, it evolves toward the same tetragonal saddle point that it reached in shear. In Mo, the symmetry break occurs after the point of maximum tensile stress has been passed, so the ideal strength is associated with the fcc shear. In Mo, the symmetry break occurs after the point of maximum tensile stress has been passed, so the ideal strength is associated with the fcc extremum as in W. However,more » a Nb crystal strained in becomes orthorhombic at tensile stress below the ideal strength. The ideal tensile strength of Nb is associated with the tetragonal saddle point and is caused by failure in shear rather than tension. In dimensionless form, the ideal shear and tensile strengths of Mo (tau* = tau-sub m/G111 = 0.12 sigma* = sigma-sub m/E100 = 0.078) are essentially identical to those previously calculated for W. Nb is anomalous. Its dimensionless shear strength is unusually high, tau* = 0.15, even though the saddle-point structure that causes it is similar to that in Mo and W, while its dimensionless tensile strength, sigma* = 0.079, is almost the same as that of Mo and W, even though the saddle-point structure is quite different.« less
198 citations
TL;DR: Polymer-stabilized tetragonal ZrO(2) nanopowders with average size of ca.
Abstract: Polymer-stabilized tetragonal ZrO2 nanopowders with average size of ca. 2.0 nm have been prepared by microwave heating in an aqueous solution containing Zr(NO3)4·5H2O, PVA, and NaOH. The photoluminescence of the synthesized ZrO2 fine particles has been investigated.
188 citations
TL;DR: In this paper, the tetragonal (α) −orthorhombic (β) −monoclinic (γ) transitions in nanometric tungsten oxide samples were investigated.
175 citations
TL;DR: In this paper, the perovskite structure of Pb(Zn1/3Nb2/3)O3 (PZN) ceramics was stabilized by adding a Ti-rich side tetragonal Pb (Zr0.47Ti0.53) O3 across the morphotropic phase boundary (MPB).
Abstract: The perovskite structure of Pb(Zn1/3Nb2/3)O3 (PZN) ceramics was stabilized by adding a Ti-rich side tetragonal Pb(Zr0.47Ti0.53)O3 (PZT) across the morphotropic phase boundary (MPB). The 0.5 PZN–0.5 PZT specimen was found to have a two-phase zone, having a high piezoelectric coefficient, d33 (430 pC/N), an electromechanical coupling factor, kp (0.67), a field-induced strain, S (0.24% at 2 kV/mm), and a remnant polarization, Pr (27 μC/cm2). A phase transition from a rhombohedral to tetragonal phase occurred when a relatively low electrical field was applied to the specimen. This transformation occurred only when the rhombohedral phase coexisted with an equal amount of the tetragonal phase of the perovskite structure. Small rhombohedral domains, which were present around the relatively large tetragonal domains, transformed as a result of the applied field. The excellent electromechanical properties at the MPB composition are attributed to this phase transition in the PZN based ceramics.
TL;DR: In this paper, the phase evolution of zirconia (ZrO2), sulfated ZrO 2 and yttrium oxide incorporated Zr O 2 from the tetrahedral phase to the monoclinic phase was studied using UV Raman spectroscopy, visible Raman Spectroscopy and x-ray diffraction (XRD).
Abstract: The phase evolution of zirconia (ZrO2), sulfated zirconia (SO42−/ZrO2) and yttrium oxide incorporated zirconia (Y2O3–ZrO2) from the tetrahedral phase to the monoclinic phase was studied using UV Raman spectroscopy, visible Raman spectroscopy and x-ray diffraction (XRD). It is clearly observed that there are discrepancies between the results from the UV Raman spectra, visible Raman spectra and XRD patterns. The phase change from tetragonal to monoclinic is always earlier or at lower calcination temperatures as observed by UV Raman spectroscopy than by visible Raman spectroscopy and XRD. UV Raman spectroscopy is found to be more sensitive at the surface region while visible Raman spectroscopy and XRD supply the information mainly from the bulk. The inconsistency in the results from the three techniques suggests that the phase transformation of zirconia starts from its surface region and then gradually develops into its bulk. For SO42−/ZrO2 and Y2O3–ZrO2, the transformation from the tetragonal to the monoclinic phase is significantly retarded owing to the presence of the sulfated groups and the yttrium oxide. Particularly, the tetragonal phase of Y2O3–ZrO2 can be maintained up to 800 °C although its phase at the surface region changed into monoclinic at 500 °C. Copyright © 2002 John Wiley & Sons, Ltd.
TL;DR: In this article, a possible correlation between Raman phonons and AO4 and MnO6 unit vibrations is proposed, and the effect of spinel inversion has been also studied on MgMn2O4 quenched samples from high temperatures.
Abstract: First order Raman spectra in the region 200–800 cm−1 have been collected for AMn2O4
(A = Mn, Mg and Zn) tetragonal spinels. A possible correlation between Raman phonons and AO4 and MnO6 unit vibrations is proposed. Structural changes have been analyzed following the evolution of the Raman spectra with x for the Mg1−xMnxMn2O4 solid solution; the effect of the spinel inversion has been also studied on MgMn2O4 quenched samples from high temperatures. The results, taking into account also the X-ray diffraction and electron paramagnetic resonance data, show the influence of the Jahn–Teller effect on the Raman scattering for this class of materials.
TL;DR: In this paper, the effect of tetragonal distortions is studied, and a metastable structure is found for c/a = 0.94, in agreement with experiments, reinforced by considering volume expansions around the experimental values for several variants.
Abstract: A major challenge for the study of the magnetically shape-controlled memory alloys Ni–Mn–Ga is the structural search for their variants. We report studies of the variants of Ni2MnGa alloys from a theoretical point of view by means of density functional calculations using the generalized gradient approximation. The effect of tetragonal distortions is studied, and a metastable structure is found for c/a = 0.94, in agreement with experiments. The c/a < 1 minimum is reinforced by considering volume expansions around the experimental values for several variants. After distortion, the electron density is redistributed around the Ni atoms as shown by neutron scattering experiments. The previous disagreement between the theoretical spin density and the experimental neutron scattering is explained. In addition, elastic constants and x-ray absorption spectra are calculated in order to encourage measurements of these quantities. (Some figures in this article are in colour only in the electronic version)
TL;DR: In this paper, the influence of cation order-disorder phenomena on the crystal structure, magnetic and electrical transport properties of new CMR perovskites for LBaMn 2 O 6 - γ (L=Pr, Nd, Sm, Eu, Gd, Tb) series has been investigated.
Abstract: Influence of cation order-disorder phenomena on the crystal structure, magnetic, and electrical transport properties of new CMR perovskites for LBaMn 2 O 6 - γ (L=Pr, Nd, Sm, Eu, Gd, Tb) series has been investigated. For each rare-earth ion three compounds have been synthesized by the topotactic reduction-oxidation method. Structural investigations have shown the oxygen-stoichiometry LBaMn 2 O 6 compound obtained in air to be cubic with disordered L 3 + and Ba 2 + cations whereas the oxygen-deficient LBaMn 2 O 5 is tetragonal with ordered L 3 + and Ba 2 + and alternate stacking of rare earth and barium containing layers along c. This crystal structure is similar to the YBaCuFeO 5 related one. Another form of oxygen-stoichiometry LBaMn 2 O 6 compound obtained by reoxidation of oxygen-deficient LBaMn 2 O 5 is also tetragonal and retains the ordering of L 3 + and Ba 2 + cations. It is notable that the reoxidized EuBaMn 2 O 6 compound has an orthorhombic unit cell. It is observed that this type of cation ordering leads to considerable increase of transition temperature to paramagnetic state. For example, disordered EuBaMn 2 O 6 compound has magnetic properties similar to spin glass and shows freezing temperature of magnetic moments T f 40 K while ordered EuBaMn 2 O 6 is an inhomogeneous ferromagnet with Curie point T C 260 K. Electrical resistivity behavior correlates with magnetization. Below the T C the Pr, Nd, Sm based compounds undergo a transition to metallic state and demonstrate a peak of magnetoresistance. It is supposed that the remarkable changing of the magnetic and electrical properties of the reoxidized compounds is a consequence of the L/Ba ordering and can be explained on the base of the Goodenough-Kanamori rules for 180° indirect superexchange interactions taking into account an ion size effect in A sublattice of perovskite.
TL;DR: In this paper, the authors synthesize, for the first time, using sol−gel technique and without doping any trivalent impurities, monodispersed, spherical ZrO2 particles in size range of ∼500−600 nm, exhibiting metastable tetragonal crystal structure at room temperature.
Abstract: We synthesize, for the first time, using sol−gel technique and without doping any trivalent impurities, monodispersed, spherical ZrO2 particles in size range of ∼500−600 nm, exhibiting metastable tetragonal crystal structure at room temperature. It is revealed using high-resolution transmission electron microscopy that “hard-aggregates” forming tendency of ZrO2 nanocrystallites of size ∼45 nm is responsible for stabilizing the high-temperature metastable tetragonal phase, at room temperature, within large sized (∼500−600 nm) undoped ZrO2 particles.
TL;DR: In this article, a template-engaged topotactic reaction was used to synthesize single-crystalline Ag2Se nanowires from trigonal selenium.
Abstract: Single-crystalline Ag2Se nanowires have been successfully synthesized through a template-engaged topotactic reaction in which nanowires of trigonal selenium were transformed into Ag2Se by reacting with aqueous AgNO3 solutions at room temperature (RT). An interesting size-dependent transition between two crystal structures has also been observed for this newly synthesized one-dimensional system: The Ag2Se nanowires adopted a tetragonal structure when their diameters were less than ∼40 nm; an orthorhombic structure was found to be more favorable as the diameter of these nanowires was increased beyond 40 nm. Since this reaction can be carried out at ambient pressure and temperature, it should be straightforward to scale up the entire process for the high-volume production of Ag2Se nanowires with well-controlled sizes and crystal structures. These highly uniform nanowires of single-crystalline Ag2Se are potentially useful as photosensitizers, superionic conductors, magnetoresistive compounds, or thermoelectric materials. This work also represents the first demonstration of a template-engaged process capable of generating single-crystalline nanowires from the solution-phase and at RT.
TL;DR: In this article, a detailed Rietveld analysis of x-ray powder diffraction data of Pb(ZrxTi1−x)O3 (PZT) compositions across the morphotropic phase boundary (MPB) region was carried out.
Abstract: We have carried out a detailed Rietveld analysis of x-ray powder diffraction data of Pb(ZrxTi1−x)O3 (PZT) compositions across the morphotropic phase boundary (MPB) region (x=0.515, 0.520, 0.525, 0.530). It is shown that the structure of PZT is pure tetragonal for x⩽0.515 with space group P4mm. In the MPB region, 0.515
TL;DR: Structural evidence is presented that the disorder of the acetic acid of crystallization induces sizable distortion of the Mn(III) sites, giving rise to six different isomers, which leads to an improved simulation of electron paramagnetic resonance spectra and justifies the tunnel splitting distribution derived from the field sweep rate dependence of the hysteresis loops.
Abstract: The problem of the role of transverse fields in Mn12-acetate, a molecular nanomagnet, is still open. We present structural evidences that the disorder of the acetic acid of crystallization indices sizeable distortion of the Mn(III) sites, giving rise to six different isomers, four of them with symmetry lower than tetragonal. Using a ligand field approach the effect of the structure modifications on the second order transverse magnetic anisotropy, forbidden in tetragonal symmetry, has been evaluated. The order of magnitude of the quadratic transverse anisotropies well agree with the values derived by the analysis of the field sweep dependence of the hysteresis loops performed by Mertes et al. ( Phys. Rev. Lett 87, 227205 (2001)) and allows to better simulate the EPR spectra.
TL;DR: In this paper, the effect of composition and microstructure on magnetic and electrical properties was investigated along with scanning electron microscopy (SEM) along with X-ray diffraction.
TL;DR: In this article, the phase transformation of tetragonal to monoclinic is accompanied by significant volume expansion, so this transition generally results in cracking and contributes to the failure of the TBC system.
Abstract: Partially stabilized zirconia (PSZ) is an attractive material for thermal barrier coatings. Zirconia exists in three crystallographic phases: cubic, tetragonal and monoclinic. In particular, the phase transformation of tetragonal to monoclinic is accompanied by significant volume expansion, so this transition generally results in cracking and contributes to the failure of the TBC system. Both plasma-sprayed ZrO2–8Y2O3 (YSZ) and ZrO2–25CeO2–2.5Y2O3 (CYSZ) coatings were isothermally heat-treated at 1300 and 1500 °C for 100 h and cooled at four different cooling rates. The monoclinic phase was not evident in all CYSZ samples annealed at 1300 and 1500 °C. In the 1500 °C heat-treated specimens, YSZ contains some monoclinic phase, while none exists in the 1300 °C heat-treated YSZ coating. The difference in phase transformation behavior between YSZ and CYSZ results from the degree of stabilization of the initial composition and the various cation radii. For YSZ, the different phase transformation behavior at the two temperatures is due to the stabilizing concentration of high-temperature phases and grain growth. For YSZ annealed at 1500 °C for 100 h, the amount of monoclinic phase increased with the slower cooling rate. High oxygen vacancy, formed during high-temperature holding, remained at room temperature due to a fast cooling rate. The extra oxygen vacancy at room temperature displaces an oxygen ion from the equilibrium position in the tetragonal phase and functions as a cubic stabilizer, so the tetragonal–monoclinic transformation is suppressed.
TL;DR: Sr2CoMoO6 perovskite has been prepared in polycrystalline form by thermal treatment, in air, of previously decomposed citrate precursors as discussed by the authors.
Abstract: Sr2CoMoO6 perovskite has been prepared in polycrystalline form by thermal treatment, in air, of previously decomposed citrate precursors. This material has been studied by X-ray (XRD) and neutron powder diffraction (NPD), thermal analysis, and magnetic, magnetotransport, and Hall effect measurements. At room temperature, the crystal structure is tetragonal with a space group I4/m, with a = 5.565 03(5) and c = 7.948 10(8) A. The crystal contains alternating CoO6 and MoO6 octahedra, tilted by 6.8° in the basal ab plane. Magnetic measurements indicate an antiferromagnetic ordering below TN = 37 K. As prepared, the sample is an electrical insulator. The topotactic reduction of the stoichiometric sample, in H2/N2 flows, leads to oxygen-deficient double perovskites, Sr2CoMoO6-δ, δ = 0.03 and 0.14. The magnetic behavior of the reduced samples suggests the presence of ferromagnetic domains characterized by Curie temperatures of TC = 350−370 K. The conductivity dramatically increases upon H2 reduction; the number ...
TL;DR: In this article, the structure of WO3 was studied in fine temperature steps, from room temperature to 1000 °C, by means of very high-resolution neutron powder diffraction, and it was confirmed that the sample used was single-phase monoclinic in space group P21/n at room temperature.
Abstract: The structures of tungsten trioxide, WO3, have been studied in fine temperature steps, from room temperature to 1000 °C, by means of very high-resolution neutron powder diffraction. It was confirmed that the sample used was single-phase monoclinic in space group P21/n at room temperature. In addition to this monoclinic structure, the structures observed were an orthorhombic structure in Pbcn from about 350 to 720 °C, another monoclinic structure in P21/c from about 720 to 800 °C, a tetragonal structure in space group P4/ncc from 800 to 900 °C, and above 900 °C a second tetragonal structure in P4/nmm. The transformation from the Pbcn orthorhombic to the P21/c monoclinic structure was certainly discontinuous, and indeed just above 720 °C two-phase mixtures were observed. The other transitions were continuous or nearly so, all three being apparently tricritical in nature. The sequence of phases, and nature (continuous or otherwise) of the transitions between them, can be well understood by reference to the results from a group theoretical analysis.
TL;DR: A detailed characterization of the structures and phase transitions occurring across this series as a function of temperature has been made in this article, where room-temperature refinements have revealed a rhombohedral phase, space group R3c for x=0, 0.2, and 0.4, which exhibits an antiphase, a −a−a− oxygen tilt system with parallel cation displacements along [111]p.
Abstract: Rietveld neutron powder profile analysis of the (Na1−xKx)0.5Bi0.5TiO3 (NKBT) series (x=0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0) is reported over the temperature range 293–993 K. A detailed characterization of the structures and phase transitions occurring across this series as a function of temperature has been made. Room-temperature refinements have revealed a rhombohedral phase, space group R3c for x=0, 0.2, and 0.4, which exhibits an antiphase, a−a−a− oxygen tilt system with parallel cation displacements along [111]p. An intermediate zero-tilt rhombohedral phase, space group R3m possessing cation displacements along [111]p, has been established for x=0.5 and 0.6. At the potassium-rich end of the series at x=0.8 and 1.0, a tetragonal phase, space group P4mm is observed possessing cation displacements along [001]. At the sodium-rich end of the series for x=0.2, the unusual tetragonal structure with space group P4bm is seen for Na0.5Bi0.5TiO3 which possesses a combination of in-phase a0a0c+ tilts and antiparallel cation displacements along the polar axis. Temperature-induced phase transitions are reported and structural modifications are discussed.
TL;DR: In this paper, the lattice constants, c/a axial ratios, and cell volumes indicate continuous changes from orthorhombic to cubic through a tetragonal phase.
Abstract: Structure refinements of solid solutions of (Ca 1 - x Sr x )TiO 3 (x = 0.0, 0.25, 0.5, 0.6, 0.65, and 1.0) were undertaken using single crystals at ambient conditions. Their lattice constants, c/a axial ratios, and cell volumes indicate continuous changes from orthorhombic to cubic through a tetragonal phase. The orthorhombic structure is continuous between x = 0.0 and x = 0.6, and a phase at x = 0.65 shows a tetragonal structure with space group I4/mcm. With increasing Sr substitution, the symmetry changes to cubic with Pm3m space group. A-O and B-O distances in ABO 3 perovskite were determined as a function of the composition of the A cation (Ca and Sr). Tilting and rotation angles of the TiO 6 octahedral linkage with x of (Ca 1 - x Sr x )TiO 3 were also evaluated. Single-crystal structure refinements of Ca 0 . 3 5 Sr 0 . 6 5 TiO 3 perovskite at 3.5, 4.1, and 7.0 GPa at 300 K were carried out using a diamond anvil cell. The tetragonal phase transforms to an orthorhombic structure with space group Pbnm at 3.5 GPa. The polymorphic transition of V I I I A 2 + V I B 4 + O 3 perovskites under compression is discussed.
TL;DR: In this paper, the results of an investigation of the ultrahigh vacuum reactive magnetron sputtering of Ta as a function of the N2 fraction fN2 in mixed Ar/N2 discharges together with the phase composition and microstructure of TaNx layers grown on MgO(001) and oxidized Si(001).
TL;DR: In this article, ultra thin films of ZrO2 were synthesized on soda lime glass and SnO2-coated glass, using ZrCl4 and H2O precursors by atomic layer deposition (ALD), a sequential CVD technique allowing the formation of dense and homogeneous films.
TL;DR: In this paper, a mixed approach was used to study Pd clusters on the MgO(100) surface, where a semi-empirical potential for the metal bonding within the cluster, and a potential fitted to ab initio calculations for metal-oxide interaction, was studied.
Abstract: Using a mixed approach: a semiempirical potential for the metal bonding within the cluster, and a potential fitted to ab initio calculations for the metal-oxide interaction, we have studied Pd clusters deposited on the MgO(100) surface. Focusing our attention on the experimentally observed pyramidal form of the Pd deposits, we have analyzed the evolution of their morphology and atomic structure as a function of cluster size. In agreement with the experimental results, we find the ``flattened'' pyramids with truncated edges being energetically the most stable. We also observe a systematic tetragonal deformation of Pd at the interface, consisting of a lateral dilation of the lattice parameter (matching the lattice parameter of the substrate), accompanied by a reduction of the vertical separation between the Pd layers. As the size of Pd cluster increases, the lattice mismatch is no longer perfectly accommodated by the dilation of the Pd deposit, and a series of subsequent structural transitions within the deposit release partially its strain, driving to relatively well localized small zones where Pd atoms do not coincide with the preferential adsorption site of Pd on the MgO(100) surface. They can be seen as dislocation precursors giving a clear superstructure pattern at the interface.
TL;DR: In this article, high-resolution synchrotron X-ray diffraction measurements were performed at 20-46 GPa on CaSiO3 perovskite (Ca-pv) synthesized in a laser heated diamond cell.
Abstract: [1] High-resolution synchrotron X-ray diffraction measurements were performed at 20–46 GPa on CaSiO3 perovskite (Ca-pv) synthesized in a laser heated diamond cell. After heating, we observed peak splittings for the cubic 200 and 211 diffraction lines, attributable to a tetragonal distortion of Ca-pv. The bulk modulus of the tetragonal phase is 255 ± 5 GPa for K0T′ = 4. The observed intensities and d-spacings of the split lines indicate that the c-axis is shorter than the a-axes (c/a = 0.993 − 0.996). This is compatible with either SiO6 octahedron rotation around the a-axes or SiO6 octahedron distortion (shorter Si-O bonds along the c-axis than the a-axes), provided that the observed phase has a tetragonal unit cell. These structural distortions in Ca-pv can affect its physical properties and capacity for large cations.
TL;DR: In this article, the authors used the Landau-Ginzburg-Devonshire approach to calculate the longitudinal piezoelectric coefficient in an arbitrary direction, d33*(θ), as a function of temperature in tetragonal BaTiO3 crystals.
Abstract: Using the Landau–Ginzburg–Devonshire approach, the longitudinal piezoelectric coefficient in an arbitrary direction, d33*(θ), was calculated as a function of temperature in tetragonal BaTiO3 crystals. The direction along which d33*(θ) is maximum is a function of piezoelectric dij coefficients referred to the crystallographic coordinate system. Below a critical ratio of the shear and longitudinal coefficients, d15/d33, the maximum d33*(θ) lies along the [001] axis. As the low-temperature orthorhombic phase is approached on cooling, the d15 increases, reflecting softening of the lattice along the axis of the incipient orthorhombic distortion, and the direction of maximum d33*(θ) deviates significantly from the [001] axis. Our results suggest that the enhanced d33*(θ) coefficient along a direction other than the polar axis recently reported in some ferroelectrics is at least in part controlled by these intrinsic lattice effects.