Showing papers on "Orthorhombic crystal system published in 2011"
TL;DR: In this article, structural and electrical evidence for a ferroelectric phase in yttrium doped hafnium oxide thin films is presented, based on X-ray diffraction.
Abstract: Structural and electrical evidence for a ferroelectric phase in yttrium doped hafnium oxide thin films is presented. A doping series ranging from 2.3 to 12.3 mol% YO1.5 in HfO2 was deposited by a thermal atomic layer deposition process. Grazing incidence X-ray diffraction of the 10 nm thick films revealed an orthorhombic phase close to the stability region of the cubic phase. The potential ferroelectricity of this orthorhombic phase was confirmed by polarization hysteresis measurements on titanium nitride based metal-insulator-metal capacitors. For 5.2 mol% YO1.5 admixture the remanent polarization peaked at 24 μC/cm2 with a coercive field of about 1.2 MV/cm. Considering the availability of conformal deposition processes and CMOS-compatibility, ferroelectric Y:HfO2 implies high scaling potential for future, ferroelectric memories.
499 citations
TL;DR: Two unexpected orthorhombic high-pressure structures Aba2-40 and Cmca-56 are reported, by using a newly developed particle swarm optimization technique on crystal structure prediction, and it is predicted that a local trigonal planar structural motif adopted by CmCA-56 exists in a wide pressure range of 85-434 GPa, favorable for the weak metallicity.
Abstract: Under high pressure, "simple" lithium (Li) exhibits complex structural behavior, and even experiences an unusual metal-to-semiconductor transition, leading to topics of interest in the structural polymorphs of dense Li. We here report two unexpected orthorhombic high-pressure structures Aba2-40 (40 atoms/cell, stable at 60-80 GPa) and Cmca-56 (56 atoms/cell, stable at 185-269 GPa), by using a newly developed particle swarm optimization technique on crystal structure prediction. The Aba2-40 having complex 4- and 8-atom layers stacked along the b axis is a semiconductor with a pronounced band gap >0.8 eV at 70 GPa originating from the core expulsion and localization of valence electrons in the voids of a crystal. We predict that a local trigonal planar structural motif adopted by Cmca-56 exists in a wide pressure range of 85-434 GPa, favorable for the weak metallicity.
472 citations
TL;DR: A new noncentrosymmetric (NCS) and polar material containing two lone-pair cations, Bi(3+) and I(5+), and exhibiting an Aurivillius-type (Bi(2)O(2))(2+) layer has been synthesized and structurally characterized.
Abstract: A new noncentrosymmetric (NCS) and polar material containing two lone-pair cations, Bi3+ and I5+, and exhibiting an Aurivillius-type (Bi2O2)2+ layer has been synthesized and structurally characterized. The material, BiO(IO3), exhibits strong second-harmonic generation (SHG), ∼12.5 × KDP (or ∼500 × α-SiO2), using 1064 nm radiation, and is found in the NCS polar orthorhombic space group Pca21 (No. 29). The structure consists of (Bi2O2)2+ cationic layers that are connected to (IO3)− anions. The macroscopic polarity, observed along the c-axis direction, may be attributed to the alignment of the IO3 polyhedra. In addition to the crystal structure and SHG measurements, polarization and piezoelectric measurements were performed, as well as electronic structure analysis.
389 citations
TL;DR: In this paper, phase transitions in ferroelectric silicon doped hafnium oxide (FE-Si:HfO2) were investigated by temperature dependent polarization and x-ray diffraction measurements.
Abstract: We investigated phase transitions in ferroelectric silicon doped hafnium oxide (FE-Si:HfO2) by temperature dependent polarization and x-ray diffraction measurements. If heated under mechanical confinement, the orthorhombic ferroelectric phase reversibly transforms into a phase with antiferroelectric behavior. Without confinement, a transformation into a monoclinic/tetragonal phase mixture is observed during cooling. These results suggest the existence of a common higher symmetry parent phase to the orthorhombic and monoclinic phases, while transformation between these phases appears to be inhibited by an energy barrier.
282 citations
TL;DR: In this article, the authors identify an orthorhombic carbon polymorph in Pnma symmetry that has the lowest enthalpy among proposed cold-compressed graphite phases.
Abstract: We identify by ab initio calculations an orthorhombic carbon polymorph in Pnma symmetry that has the lowest enthalpy among proposed cold-compressed graphite phases. This new phase contains alternating zigzag and armchair buckled carbon sheets transformed via a one-layer by three-layer slip mechanism. It has a wide indirect band gap and a large bulk modulus that are comparable to those of diamond. Its simulated x-ray diffraction pattern best matches the experimental data. Pressure plays a key role in lowering the kinetic barrier during the phase conversion process. These results provide a comprehensive understanding and an excellent account for experimental findings.
277 citations
TL;DR: In this article, the crystal structures of and phase transitions in the Li3PS4, which is part of the thio-LISICON (LIthium Super Ionic CONductor) family, were studied using high-temperature synchrotron X-ray diffraction measurements and thermal analysis.
266 citations
TL;DR: The correlation between stripe order, superconductivity, and crystal structure in La{sub 2-x}Ba{sub x}CuO{sub 4} single crystals have been studied by means of x-ray and neutron diffraction as well as static magnetization measurements as mentioned in this paper.
Abstract: The correlations between stripe order, superconductivity, and crystal structure in La{sub 2-x}Ba{sub x}CuO{sub 4} single crystals have been studied by means of x-ray and neutron diffraction as well as static magnetization measurements The derived phase diagram shows that charge stripe order (CO) coexists with bulk superconductivity in a broad range of doping around x=1/8, although the CO order parameter and correlation length fall off quickly for x {ne} 1/8 Except for x=0155, the onset of CO always coincides with the transition between the orthorhombic and the tetragonal or less orthorhombic low-temperature structures The CO transition evolves from a sharp drop at low x to a more gradual transition at higher x, eventually falling below the structural phase boundary for optimum doping With respect to the interlayer CO correlations, we find no qualitative change of the stripe stacking order as a function of doping, and in-plane and out-of-plane correlations disappear simultaneously at the transition Similarly to the CO, the spin stripe order (SO) is also most pronounced at x=1/8 Truly static SO sets in below the CO and coincides with the first appearance of in-plane superconducting correlations at temperatures significantly above the bulk transition to superconductivity (SC) Indications that bulk SCmore » causes a reduction of the spin or charge stripe order could not be identified We argue that CO is the dominant order that is compatible with SC pairing but competes with SC phase coherence Comparing our results with data from the literature, we find good agreement if all results are plotted as a function of x' instead of the nominal x, where x' represents an estimate of the actual Ba content, extracted from the doping dependence of the structural transition between the orthorhombic phase and the tetragonal high-temperature phase« less
214 citations
TL;DR: New noncentrosymmetric rare-earth metal gallium thioantimonates, Ln(4)GaSbS(9) were synthesized from stoichiometric element mixtures at 950 °C by high-temperature solid-state reactions.
Abstract: New noncentrosymmetric rare-earth metal gallium thioantimonates, Ln4GaSbS9 were synthesized from stoichiometric element mixtures at 950 °C by high-temperature solid-state reactions. These compounds crystallize in orthorhombic space group Aba2 (no.41) with a = 13.799(3)−13.427(5) A, b = 14.187(3)−13.756(5) A, c = 14.323(3)−13.954(5) A, V = 2804(2)−2577 (2) A3, and Z = 8 on going from Ln = Pr to Ho. The asymmetric building units, bimetallic polar (Sb2S5) units, and dimeric (GaS4)2 tetrahedra are in-phase aligned as an infinite single anionic chain of {[(Ga2S6)(Sb2S5)]10−}∞ that is further packed in a noncentrosymmetric pseudolayer motif perpendicular to the c axis. Three of the title compounds show large powder second harmonic generation (SHG) effects at 2.05 μm, and two of them also exhibit large transparency ranges (1.75 or 0.75 to 25 μm) in the middle-IR region. Significantly, the Sm-member exhibits the strongest SHG response among sulfides to date with intensity approximately 3.8 times that of the bench...
183 citations
TL;DR: In this paper, the authors analyzed the impact of a slight orthorhombic and monoclinic distortion of the Ni 50.2 Mn 28.3 Ga 21.5 at.
174 citations
TL;DR: Detailed analysis of the optical spectra reveals an unprecedented electronic state in the ordered phase of iron arsenides, arising from an anisotropic energy gap opening below and slightly above the onset of the order.
Abstract: An ordered phase showing remarkable electronic anisotropy in proximity to the superconducting phase is now a hot issue in the field of high-transition-temperature superconductivity. As in the case of copper oxides, superconductivity in iron arsenides competes or coexists with such an ordered phase. Undoped and underdoped iron arsenides have a magnetostructural ordered phase exhibiting stripe-like antiferromagnetic spin order accompanied by an orthorhombic lattice distortion; both the spin order and lattice distortion break the tetragonal symmetry of crystals of these compounds. In this ordered state, anisotropy of in-plane electrical resistivity is anomalous and difficult to attribute simply to the spin order and/or the lattice distortion. Here, we present the anisotropic optical spectra measured on detwinned BaFe2As2 crystals with light polarization parallel to the Fe planes. Pronounced anisotropy is observed in the spectra, persisting up to an unexpectedly high photon energy of about 2 eV. Such anisotropy arises from an anisotropic energy gap opening below and slightly above the onset of the order. Detailed analysis of the optical spectra reveals an unprecedented electronic state in the ordered phase.
173 citations
TL;DR: In this article, in situ Raman spectroscopy was employed to investigate the interaction between MoO3 and 1% H2 in both N2 and synthetic air environments, while incorporating Pd as a catalyst at room temperature.
Abstract: It is known that the unique layered structure of orthorhombic MoO3 (α-MoO3) facilitates the interaction with H2 gas molecules and that the surface-to-volume ratios of the crystallites play an important role in the process. MoO3 was deposited on a wide variety of transparent substrates using thermal evaporation in order to alter the surface-to-volume ratios of the crystallites. In situ Raman spectroscopy was employed to investigate the interaction between MoO3 and 1% H2 in both N2 and synthetic air environments, while incorporating Pd as a catalyst at room temperature. This study confirmed that the layered MoO3 with a high surface-to-volume ratio facilitated the H2 gas interaction. The Raman spectroscopy studies revealed that the H+ ions mainly interacted with the doubly coordinated oxygen atoms and caused the crystal transformation from the original α-MoO3 into the mixed structure of hydrogen molybdenum bronze and substoichiometric MoO3, eventually forming oxygen vacancies and water. It was also found tha...
TL;DR: In this paper, a molybdate-based inorganic-organic hybrid disks with a highly ordered layered structure were synthesized via an acid-base reaction of white molybdic acid (MoO3·H2O) with n-octylamine (C8H17NH2) in ethanol at room temperature.
Abstract: Molybdate-based inorganic–organic hybrid disks with a highly ordered layered structure were synthesized via an acid–base reaction of white molybdic acid (MoO3·H2O) with n-octylamine (C8H17NH2) in ethanol at room temperature. The thermal treatment of the as-obtained molybdate-based inorganic–organic hybrid disks at 550 °C in air led to formation of orthorhombic α-MoO3 nanoplates. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermal analysis (TG–DTA), Fourier-transform infrared (FT–IR) spectra, Raman spectra, and a laser-diffraction grain-size analyzer were used to characterize the starting materials, the intermediate hybrid precursors and the final α-MoO3 nanoplates. The XRD, FT–IR and TG–DTA results suggested that the molybdate-based inorganic–organic hybrid compound, with a possible composition of (C8H17NH3)2MoO4, was of a highly ordered lamellar structure with an interlayer distance of 2.306(1) nm, and the n-alkyl chains in the interlayer places took a double-layer arrangement with a tilt angle of 51° against the inorganic MoO6 octahedra layers. The SEM images indicated that the molybdate-based inorganic–organic hybrids took on a well-dispersed disk-like morphology, which differed distinctly from the severely aggregated morphology of their starting MoO3·H2O powders. During the calcining process, the disk-like morphology of the hybrid compounds was well inherited into the orthorhombic α-MoO3 nanocrystals, showing a definite plate-like shape. The α-MoO3 nanoplates obtained were of a single-crystalline structure, with a side-length of 1–2 μm and a thickness of several nanometres, along a thickness direction of [010]. The above α-MoO3 nanoplates were of a loose aggregating texture and high dispersibility. The chemical sensors derived from the as-obtained α-MoO3 nanoplates showed an enhanced and selective gas-sensing performance towards ethanol vapors. The α-MoO3 nanoplate sensors reached a high sensitivity of 44–58 for an 800 ppm ethanol vapor operating at 260–400 °C, and their response times were less than 15 s.
TL;DR: The phase confirmation and structural properties of the sample was elucidated by X-ray diffraction (XRD) method as discussed by the authors, which revealed that an increase in reaction temperature, the shape was drastically changed from one dimensional (1D) to two dimensional (2D) layered structures.
TL;DR: In this paper, the authors describe a systematic study of the hydrothermal synthesis of rare-earth orthochromites, RCrO3 (R = La, Pr, Sm, Gd, Dy, Ho, Yb, and Lu), which can be prepared in a single step by a single-step treatment of an amorphous mixed-metal hydroxide at temperatures above 300 °C upon heating around 24 h, with no post-synthesis annealing needed.
Abstract: We describe a systematic study of the hydrothermal synthesis of rare-earth orthochromites, RCrO3 (R = La, Pr, Sm, Gd, Dy, Ho, Yb, and Lu) and YCrO3. All nine of these materials can be prepared in a single step by hydrothermal treatment of an amorphous mixed-metal hydroxide at temperatures above 300 °C upon heating around 24 h, with no post-synthesis annealing needed. The as-made materials are highly crystalline powders with submicrometer particle size. In the case of LaCrO3 the addition of solution additives to the hydrothermal synthesis allows some modification of crystallite form of the material, and in the presence of sodium dodecylsulfate nanocrystalline powders are produced. Profile refinement of powder X-ray diffraction (XRD) data show that each of the RCrO3 materials adopts an orthorhombic distorted (Pbmn) perovskite structure. Detailed, magnetization studies as a function of temperature reveal the high quality of the specimens, with low temperature antiferromagnetic behavior seen by direct current...
TL;DR: The SmAPF, the smectic of fluid polar orthorhombic layers that order into a three-dimensional ferroelectric state, is reported, the highest-symmetry layered ferro electric material found to date and the highest to date.
Abstract: Macroscopic polarization density, characteristic of ferroelectric phases, is stabilized by dipolar intermolecular interactions. These are weakened as materials become more fluid and of higher symmetry, limiting ferroelectricity to crystals and to smectic liquid crystal stackings of fluid layers. We report the SmAP(F), the smectic of fluid polar orthorhombic layers that order into a three-dimensional ferroelectric state, the highest-symmetry layered ferroelectric possible and the highest-symmetry ferroelectric material found to date. Its bent-core molecular design employs a single flexible tail that stabilizes layers with untilted molecules and in-plane polar ordering, evident in monolayer-thick freely suspended films. Electro-optic response reveals the three-dimensional orthorhombic ferroelectric structure, stabilized by silane molecular terminations that promote parallel alignment of the molecular dipoles in adjacent layers.
TL;DR: In this article, the Pr3+−Yb3+ ion codoped 40SiO2−30Al2O3−18Na2O−12LaF3 glasses were synthesized by a conventional melting-quenching method.
Abstract: The Pr3+–Yb3+ ion codoped 40SiO2–30Al2O3–18Na2O–12LaF3 glasses were synthesized by a conventional melting–quenching method. Near-infrared downconversion emission with 12% quantum yield has been realized. Transparent glass ceramics containing LaF3 nanocrystals were prepared by heat treatment. X-ray diffraction and scanning electron microscopy results show that fluorides favor the formation of small crystals. Comparing the absorption and emission spectra of the glasses with that of the glass ceramics indicates that the Pr3+ ions are incorporated in priority into the LaF3 crystals, due to the similar crystal lattice. Thus, energy transfer efficiency cannot be enhanced in the present glass by crystallization. It is suggested that fluorides from TbF3 to LuF3 (including YF3) having the orthorhombic structure in aluminosilicate glass are suitable for incorporating YbF3 during the crystallization process.
TL;DR: The synthesis of perylene 3,4:9,10-tetracarboxylic acid bisimides (PBIs) dendronized with first-generation dendrons containing 0 to 4 methylenic units between the imide group and the dendRON, (3,4,5)12G1-m-PBI, is reported.
Abstract: The synthesis of perylene 3,4:9,10-tetracarboxylic acid bisimides (PBIs) dendronized with first-generation dendrons containing 0 to 4 methylenic units (m) between the imide group and the dendron, (3,4,5)12G1-m-PBI, is reported. Structural analysis of their self-organized arrays by DSC, X-ray diffraction, molecular modeling, and solid-state 1H NMR was carried out on oriented samples with heating and cooling rates of 20 to 0.2 °C/min. At high temperature, (3,4,5)12G1-m-PBI self-assemble into 2D-hexagonal columnar phases with intracolumnar order. At low temperature, they form orthorhombic (m = 0, 2, 3, 4) and monoclinic (m = 1) columnar arrays with 3D periodicity. The orthorhombic phase has symmetry close to hexagonal. For m = 0, 2, 3, 4 ,they consist of tetramers as basic units. The tetramers contain a pair of two molecules arranged side by side and another pair in the next stratum of the column, turned upside-down and rotated around the column axis at different angles for different m. In contrast, for m = ...
TL;DR: In this paper, Stannous sulfide films were prepared by chemical bath deposition in which a novel chelating reagent ammonium citrate was used to obtain homogeneous and well adhered.
TL;DR: A new potential infrared (IR) nonlinear optical (NLO) material Bi(2)(IO(4))(IO(3))(3) was synthesized by hydrothermal method and is the first noncentrosymmetric (NCS) structure containing [IO4](3-) anion.
Abstract: A new potential infrared (IR) nonlinear optical (NLO) material Bi2(IO4)(IO3)3 was synthesized by hydrothermal method. Bi2(IO4)(IO3)3 crystallizes in the chiral orthorhombic space group P212121 (No. 19) with a = 5.6831(11) A, b = 12.394(3) A, and c = 16.849(3) A. It exhibits a three-dimensional framework through a combination of the IO3, IO4, BiO8, and BiO9 polyhedra and is the first noncentrosymmetric (NCS) structure containing [IO4]3– anion. Bi2(IO4)(IO3)3 has an IR cutoff wavelength of 12.3 μm and belongs to the type 1 phase-matchable class with a moderately large SHG response of 5 × KDP, which is in good agreement with the theoretical calculations.
TL;DR: In this paper, the hardness of a new high-pressure boron phase, orthorhombic δ-gamma-B28, was measured and the results showed that B28 has the highest hardness of all known crystalline modifications of Boron.
Abstract: Measurements of the hardness of a new high-pressure boron phase, orthorhombic {\gamma}-B28, are reported. According to the data obtained, {\gamma}-B28 has the highest hardness (~50 GPa) of all known crystalline modifications of boron.
TL;DR: The La0.8Ca0.2−x□xMnO3 compounds were prepared by the solid-state reaction and X-ray diffraction (XRD) and magnetic measurements were used to investigate the calcium-vacancy effect on the physical properties as mentioned in this paper.
TL;DR: In this paper, an asymmetric electrochromic device is constructed based on this porous o-WO3 layer using an Organically Modified Silicate (ORMOSIL) based templating strategy to achieve porosity.
Abstract: Porous orthorhombic tungsten oxide (o-WO3) thin films, stabilized by nanocrystalline anatase TiO2, are obtained by a sol–gel based two stage dip coating method and subsequent annealing at 600 °C. An Organically Modified Silicate (ORMOSIL) based templating strategy is adopted to achieve porosity. An asymmetric electrochromic device is constructed based on this porous o-WO3 layer. The intercalation/deintercalation of lithium ions into/from the o-WO3 layer of the device as a function of applied coloration/bleaching voltages have been studied. XRD measurements show systematic changes in the lattice parameters associated with structural phase transitions from o-WO3 to tetragonal LixWO3 (t-LixWO3) and a tendency to form cubic LixWO3 (c-LixWO3). These phase transitions, induced by the Li ions, are reversible, and the specific phase obtained depends on the quantity of intercalated/deintercalated Li. Raman spectroscopy data show the formation of t-LixWO3 for an applied potential of 1.0 V and the tendency of the system to transform to c-LixWO3 for higher coloration potentials. Optical measurements show excellent contrasts between colored and bleached states. An alternate photochromic device was constructed by sensitizing the o-WO3 layer with a ruthenium based dye. The nanocrystalline anatase TiO2 in the o-WO3 layer has led to an enhanced photochromic optical transmittance contrast of ∼51% in the near IR region. The combination of the photochromic and electrochromic properties of the synthesised o-WO3 layer stabilized by nanocrystalline anatase TiO2 opens up new vista for its application in energysaving smart windows.
TL;DR: In this paper, BaZrO3 changes the symmetry of the ceramics from tetragonal dominant phase with x = 0.07-0.09 to rhombohedral phase with X-ray diffraction patterns.
Abstract: 0.94(K0.4−xNa0.6BaxNb1−xZrx)O3–0.06LiSbO3 ceramics were prepared by conventional technique, and the effect of BaZrO3 on the phase transitions, dielectric, ferroelectric, and piezoelectric properties of the ceramics were investigated. The phase transitions for the ceramics were determined by the temperature dependence of dielectric properties and X-ray diffraction patterns. BaZrO3 changes the symmetry of the ceramics from tetragonal dominant phase with x = 0–0.06 to rhombohedral phase with x = 0.07–0.09. The phase transition near room temperature for the composition with x ~ 0.06 is different from previously reported phase transition between orthorhombic and tetragonal phases. It is suggested that a new morphotropic phase boundary (MPB) is constructed with both rhombohedral–orthorhombic and orthorhombic–tetragonal phase transitions near room temperature, and the enhanced piezoelectric properties (d33 = 344 pC/N and kP = 32.4% with x = 0.06) are obtained. The results indicate that the construction of new MPB is of significance for further development of KNN-based ceramics.
TL;DR: In this paper, an orthorhombic perovskite YCrO 3 phase with Mn substitute for Cr was synthesized by classical solid state reaction at 1200°C, and sintered under nitrogen atmosphere at 1500°C and 1600°C. XRD patterns analysis has revealed that for x ǫ ≥ 0.6, a second phase with a structure similar to the hexagonal YMnO3 phase appears.
Abstract: YCr 1− x Mn x O 3 (0 ≤ x ≤ 0.8) negative temperature coefficient (NTC) compositions were synthesized by classical solid state reaction at 1200 °C, and sintered under nitrogen atmosphere at 1500 °C and 1600 °C. XRD patterns analysis has revealed that for x ≤ 0.6, the structure consists of a solid solution of an orthorhombic perovskite YCrO 3 phase with Mn substitute for Cr. For x ≥ 0.8, a second phase with a structure similar to the hexagonal YMnO 3 phase appears. SEM images and calculated open porosity have shown that the substitution of Mn for Cr results in a decrease in porosity. Whatever the sintering temperature, the electrical characterizations (between 25 and 900 °C) have shown that the increase in the manganese content involves the decrease in both resistivity and material constant B (parameter which characterizes the thermal sensitivity of material) when x ≤ 0.6. The magnitude order of the resistivity at 25 °C is of 10 4 –10 8 Ω cm and activation energies vary from 0.28 to 0.99 eV at low and high temperatures, respectively.
TL;DR: The phase equilibria and reaction temperatures in the system Al–Cu were re-investigated by a combination of optical microscopy, powder X-ray diffraction (XRD) at ambient and elevated temperature, differential thermal analysis (DTA) and scanning electron microscopy (SEM).
TL;DR: Perovskite-type PbNiO(3) is the first example of the Pb(4+)M(2+)O( 3) series, and the first examples of the perovskites containing a tetravalent A-site cation without lone pair electrons.
Abstract: We synthesized two high-pressure polymorphs PbNiO3 with different structures, a perovskite-type and a LiNbO3-type structure, and investigated their formation behavior, detailed structure, structural transformation, thermal stability, valence state of cations, and magnetic and electronic properties. A perovskite-type PbNiO3 synthesized at 800 °C under a pressure of 3 GPa crystallizes as an orthorhombic GdFeO3-type structure with a space group Pnma. The reaction under high pressure was monitored by an in situ energy dispersive X-ray diffraction experiment, which revealed that a perovskit-type phase was formed even at 400 °C under 3 GPa. The obtained perovskite-type phase irreversibly transforms to a LiNbO3-type phase with an acentric space group R3c by heat treatment at ambient pressure. The Rietveld structural refinement using synchrotron X-ray diffraction data and the XPS measurement for both the perovskite- and the LiNbO3-type phases reveal that both phases possess the valence state of Pb4+Ni2+O3. Perovs...
TL;DR: Thermogravimetric analysis on metastable MoO3 revealed that the hexagonal phase was stable up to 430 °C and above this temperature complete transformation into a highly stable orthorhombic phase was achieved.
Abstract: Hexagonal molybdenum oxide (h-MoO3) was synthesized by a solution based chemical precipitation technique. Analysis by X-ray diffraction (XRD) confirmed that the as-synthesized powder had a metastable hexagonal structure. The characteristic vibrational band of Mo–O was identified from Fourier transform infrared spectroscopy (FT-IR). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images clearly depicted the morphology and size of h-MoO3. The morphology study showed that the product comprises one-dimensional (1D) hexagonal rods. From the electron energy loss spectroscopy (EELS) measurement, the elemental composition was investigated and confirmed from the characteristic peaks of molybdenum and oxygen. Thermogravimetric (TG) analysis on metastable MoO3 revealed that the hexagonal phase was stable up to 430 °C and above this temperature complete transformation into a highly stable orthorhombic phase was achieved. The optical band gap energy was estimated from the Kubelka–Munk (K–M) function and was found to be 2.99 eV. Finally, the ethanol vapor-sensing behavior was investigated and the sensing response was found to vary linearly as a function of ethanol concentration in the parts per million (ppm) range.
TL;DR: In this paper, X-ray diffraction patterns indicate that the nanocrystalline La1−xBaxFeO3 powders are perovskite phase with orthorhombic structure.
TL;DR: This work investigates the in situ Raman spectra changes of WO(3) films of different crystal phases, while incorporating Pd catalysts, at elevated temperatures in the presence of H(2) gas, and suggests that the changes of Rama under such conditions to be mainly a function of the crystal phase.
Abstract: It is well known that WO3 interacts efficiently with H2 gas in the presence of noble metals (such as Pd, Pt and Au) at elevated temperatures, changing its optical behaviors; and that its crystallinity plays an important role in these interactions. For the first time, we investigated the in situRaman spectra changes of WO3 films of different crystal phases, while incorporating Pd catalysts, at elevated temperatures in the presence of H2. The Pd/WO3 films were prepared using RF sputtering and subsequently annealed at 300, 400 and 500 °C in air in order to alter the dominant crystal phase. The films were then characterized using SEM, XRD, XPS, and both UV-VIS and Raman spectroscopy. In order to fundamentally study the process, the measurements were conducted when films were interacting with 1% H2 in synthetic air at elevated sample temperatures (20, 60, 100 and 140 °C). We suggest that the changes of Raman spectra under such conditions to be mainly a function of the crystal phase, transforming from monoclinic to a mix phase of monoclinic and orthorhombic achieved via increasing the annealing temperature. The as-deposited sample consistently shows similar Raman spectra responses at different operating conditions upon H2 exposure. However, increasing the annealing temperature to 500 °C tunes the optimum H2 response operating temperature to 60 °C.
TL;DR: In this article, the electronic band structure, density of states, complex dielectric function, optical absorption, and the infrared and Raman spectra of orthorhombic CaSnO{sub 3} were computed using density functional theory.