Showing papers on "Tetragonal crystal system published in 2013"
TL;DR: In this paper, the effects of annealing temperature (Tanneal) and film thickness (tf) on the crystal structure and ferroelectric properties of Hf 0.5Zr0.5O2 films were examined.
Abstract: The effects of annealing temperature (Tanneal) and film thickness (tf) on the crystal structure and ferroelectric properties of Hf0.5Zr0.5O2 films were examined. The Hf0.5Zr0.5O2 films consist of tetragonal, orthorhombic, and monoclinic phases. The orthorhombic phase content, which is responsible for the ferroelectricity in this material, is almost independent of Tanneal, but decreases with increasing tf. In contrast, increasing Tanneal and tf monotonically increases (decreases) the amount of monoclinic (tetragonal) phase, which coincides with the variations in the dielectric constant. The remanant polarization was determined by the content of orthorhombic phase as well as the spatial distribution of other phases.
506 citations
TL;DR: These experiments establish that compounds violating chemical intuition can be thermodynamically stable even in simple systems at nonambient conditions.
Abstract: Sodium chloride (NaCl), or rocksalt, is well characterized at ambient pressure. As a result of the large electronegativity difference between Na and Cl atoms, it has highly ionic chemical bonding (with 1:1 stoichiometry dictated by charge balance) and B1-type crystal structure. By combining theoretical predictions and diamond anvil cell experiments, we found that new materials with different stoichiometries emerge at high pressures. Compounds such as Na3Cl, Na2Cl, Na3Cl2, NaCl3, and NaCl7 are theoretically stable and have unusual bonding and electronic properties. To test this prediction, we synthesized cubic and orthorhombic NaCl3 and two-dimensional metallic tetragonal Na3Cl. These experiments establish that compounds violating chemical intuition can be thermodynamically stable even in simple systems at nonambient conditions.
408 citations
TL;DR: Magnetic field-induced strain (MFIS) of 12% was reported in ferromagnetic Ni 46Mn24Ga22Co4 Cu 4 martensite exhibiting non-modulated (NM) tetragonal crystal structure with lattice parameter ratio c / a > 1.
Abstract: Magnetic field-induced strain (MFIS) of 12% is reported in ferromagnetic Ni 46Mn24Ga22Co4 Cu 4 martensite exhibiting non-modulated (NM) tetragonal crystal structure with lattice parameter ratio c / a > 1 . The strain was measured at ambient temperature in a magnetic field of the order of 1 T. The twinning stress σ T W and the magnetic stress σ M A G were also measured and the condition for a giant MFIS observation σ T W < σ M A G was confirmed. The MFIS was achieved in NM Ni 46Mn24Ga22Co4 Cu 4 martensite by considerable lowering of the σ T W value as compared to the values for NM martensites in ternary Ni-Mn-Ga system.
328 citations
TL;DR: In this article, the structural stability of Li7La3Zr2O12 garnets is investigated, focusing on the mechanisms that result in the transformation from tetragonal to cubic symmetry, and the natures of the high and low temperature cubic garnets are totally different: the one found above the phase transition does not involve any change in the stoichiometry, whereas the cubic phase formed at low temperature is a hydrated, lithium defective phase, due to the combined effect of water insertion into the garnet structure and the H+/Li+ exchange mechanism.
Abstract: We address the controversial issue of the structural stability of Li7La3Zr2O12 garnets, focusing on the mechanisms that result in the transformation from tetragonal to cubic symmetry. We show that undoped tetragonal Li7La3Zr2O12 not exposed to humidity at any moment undergoes a reversible phase transition to cubic symmetry at Tc ≃ 645 °C that we ascribe to lithium dynamic effects. On the other hand, a close correlation has been found between the appearance of a cubic phase between 100 and 200 °C in X-ray diffractograms and the presence of water, either in the atmosphere in which experiments are performed or already in the starting material. The natures of the high and low-temperature cubic garnets are totally different: the one found above the phase transition does not involve any change in the stoichiometry, whereas the cubic phase formed at low temperature is a hydrated, lithium defective phase, due to the combined effect of water insertion into the garnet structure and the H+/Li+ exchange mechanism. Differences in the actual compositions of the samples depending on their thermal history are corroborated by TG-MS experiments. Chemical reactions and phases formed along the thermal evolution are elucidated with the help of Raman spectroscopy.
266 citations
TL;DR: In this article, the Li ion dynamics and the structure of tetragonal Li10GeP2S12 and 7Li PFG NMR were characterized using a multitude of complementary techniques, including impedance spectroscopy, 7Li NMR relaxometry, X-ray diffraction and electron diffraction.
Abstract: Tetragonal Li10GeP2S12 (LGPS) is the best solid Li electrolyte reported in the literature. In this study we present the first in-depth study on the structure and Li ion dynamics of this structure type. We prepared two different tetragonal LGPS samples, Li10GeP2S12 and the new compound Li7GePS8. The Li ion dynamics and the structure of these materials were characterized using a multitude of complementary techniques, including impedance spectroscopy, 7Li PFG NMR, 7Li NMR relaxometry, X-ray diffraction, electron diffraction, and 31P MAS NMR. The exceptionally high ionic conductivity of tetragonal LGPS of ∼10−2 S cm−1 is traced back to nearly isotropic Li hopping processes in the bulk lattice of LGPS with EA ≈ 0.22 eV.
225 citations
TL;DR: In this paper, the authors reported synthesis and superconductivity at 3.7 K in REO0.5F 0.5BiS2 using vacuum encapsulation technique.
Abstract: We report synthesis and superconductivity at 3.7 K in PrO0.5F0.5BiS2. The newly discovered material belongs to the layered sulfide based REO0.5F0.5BiS2 compounds having a ZrCuSiAs-type structure. The bulk polycrystalline compound is synthesized by the vacuum encapsulation technique at 780 ∘C in a single step. Detailed structural analysis has shown that the as synthesized PrO0.5F0.5BiS2 is crystallized in a tetragonal P4/nmm space group with lattice parameters a=4.015(5) A, c=13.362(4) A. Bulk superconductivity is observed in PrO0.5F0.5BiS2 below 4 K from magnetic and transport measurements. Electrical transport measurements showed superconducting transition temperature (Tc) onset at 3.7 K and Tc(ρ=0) at 3.1 K. The hump at Tc related to the superconducting transition is not observed in the heat capacity measurement and rather a Schottky-type anomaly is observed at below ∼6 K. The compound is slightly semiconducting in a normal state. Isothermal magnetization (MH) exhibited typical type II behavior with a lower critical field (Hc1) of around 8 Oe.
194 citations
TL;DR: To better understand the interface conductivity, scanning superconducting quantum interference device microscopy is used to image the magnetic field locally generated by current in an interface and finds that the current flowed in conductive narrow paths oriented along the crystallographic axes, embedded in a less conductive background.
Abstract: The emergence of conductivity at the {001} interface of LaAlO3 and SrTiO3 is one of the more celebrated examples of interface engineering. Using a microscopy approach based on a sensitive magnetometry probe, it is now shown that narrow paths of enhanced conductivity occur along the crystallographic axes of the oxide structures.
193 citations
TL;DR: BiVO4 powders with hierarchical structures were prepared by the microwave hydrothermal method at different pHs, using Bi(NO3)3·5H2O and NH4VO3 as raw materials and the corresponding relationship among pH values of the precursor, crystalline phase, morphology, and photocatalytic performance was discussed.
Abstract: BiVO4 powders with hierarchical structures were prepared by the microwave hydrothermal method at different pHs, using Bi(NO3)3·5H2O and NH4VO3 as raw materials. The results show that, when the pH value of the precursor is 0.59, the as-prepared powders are monoclinic BiVO4 crystals with octahedron and decahedron morphologies. Spherical and polyhedral BiVO4 with particle sizes in the range of 2–4 μm can be prepared under the strong acid condition (pH = 0.70–1.21) and possess a mixed crystal consisting of tetragonal and monoclinic phases, whereas rodlike and dendritic BiVO4 with a pure monoclinic phase can be obtained within a very wide pH range (pH = 4.26–9.76). The phase transformation from tetragonal phase to monoclinic phase occurs at pH 3.65. At pH >9.76, the powders are the nonstoichiometric crystals between the mixed-phase BiVO4 and non-BiVO4. The photocatalytic efficiencies were evaluated by the degradation of Rhodamine B (RhB) under UV and simulated sunlight irradiation. The corresponding relationsh...
192 citations
TL;DR: In this paper, a process for deposition of tetragonal Cu 2 SnS 3 (CTS) thin films from methanolic precursor solution of metal-thiourea complex by direct liquid coating (DLC) is described.
173 citations
TL;DR: The plate-like single crystals of tetragonal (P4/nmm) FeSe1−x superconductors were grown using the KCl-AlCl3 flux technique in this article.
Abstract: The plate-like single crystals of tetragonal (P4/nmm) FeSe1−x superconductors were grown using the KCl–AlCl3 flux technique which produced single crystalline tetragonal samples of about 4 × 4 × 0.1 mm3 dimensions. The energy dispersive X-ray spectroscopy established a ratio of Fe : Se = 1 : 0.96 ± 0.02. The resistivity and magnetization measurements revealed a sharp superconducting transition at Tc = 9.4 K. Multiple Andreev reflections spectroscopy pointed to the existence of two-gap superconductivity with the gap values ΔL = 2.4 ± 0.2 meV and ΔS = 0.75 ± 0.1 meV at 4.2 K.
159 citations
TL;DR: In this paper, structural studies suggested a transition in phase from tetragonal to cubic symmetry with increase in Lanthanum content and Rietveld Refinement technique employed for investigation confirmed the same.
TL;DR: Comparison between the extracted charge nematic susceptibility and the elastic modulus allows us to disentangle the charge contribution to the nematic instability, and to show that charge nematics fluctuations are weakly coupled to the lattice.
Abstract: Using electronic Raman spectroscopy, we report direct measurements of charge nematic fluctuations in the tetragonal phase of strain-free Ba(Fe(1-x)Co(x))2As2 single crystals. The strong enhancement of the Raman response at low temperatures unveils an underlying charge nematic state that extends to superconducting compositions and which has hitherto remained unnoticed. Comparison between the extracted charge nematic susceptibility and the elastic modulus allows us to disentangle the charge contribution to the nematic instability, and to show that charge nematic fluctuations are weakly coupled to the lattice.
TL;DR: A continuous and gradual lattice deformation in bending nickel nanowires to a reversible shear strain as high as 34.6%, which is approximately four times that of the theoretical elastic strain limit for unconstrained loading is reported.
Abstract: The elastic strain sustainable in crystal lattices is usually limited by the onset of inelastic yielding mediated by discrete dislocation activity, displacive deformation twinning and stress-induced phase transformations, or fracture associated with flaws. Here we report a continuous and gradual lattice deformation in bending nickel nanowires to a reversible shear strain as high as 34.6%, which is approximately four times that of the theoretical elastic strain limit for unconstrained loading. The functioning deformation mechanism was revealed on the atomic scale by an in situ nanowire bending experiments inside a transmission electron microscope. The complete continuous lattice straining process of crystals has been witnessed in its entirety for the straining path, which starts from the face-centred cubic lattice, transitions through the orthogonal path to reach a body-centred tetragonal structure and finally to a re-oriented face-centred cubic structure.
TL;DR: In this article, a methodology for constructing anharmonic vibrational Hamiltonians that are parametrized from first-principles electronic-structure calculations and can be used to study high-temperature properties of crystalline materials is introduced.
Abstract: We introduce a methodology for constructing anharmonic vibrational Hamiltonians that are parametrized from first-principles electronic-structure calculations and can be used to study high-temperature properties of crystalline materials. Our method provides an accurate description of the Born-Oppenheimer potential energy surface of a crystal that can be systematically refined and is invariant to space-group symmetries of the ideal reference crystal and finite rigid-body rotations and translations. These features make it ideally suited for Monte Carlo or molecular dynamics simulations to predict finite-temperature thermodynamic properties, structural phase transitions, and thermal conductivity. We use this method to construct an anharmonic Hamiltonian for ZrH${}_{2}$, which exhibits a high-temperature cubic phase that undergoes a symmetry-breaking second-order transition to one of three equivalent tetragonal phases upon cooling. Although density functional theory predicts a zero-Kelvin dynamical instability of cubic ZrH${}_{2}$, we find via Monte Carlo simulation that the cubic phase can be anharmonically stabilized at high temperature and predict a cubic-to-tetragonal transition temperature that is in good agreement with extrapolation from experiments. We also calculate finite-temperature free energies for the cubic and tetragonal phases, finding that they are consistent with the phenomenological Landau theory of second-order phase transitions.
TL;DR: The results from this study are potentially applicable to a range of perovskite-type mixed metal oxides useful in water splitting as well as other areas of heterogeneous photocatalysis.
Abstract: Potassium niobate (KNbO3) microcubes with orthorhombic and tetragonal phases were hydrothermally prepared and characterized by powder X-ray diffraction, nitrogen adsorption–desorption, micro-Raman spectroscopy, Fourier transform infrared spectroscopy, diffuse reflectance UV-visible spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The photoreactivity of the as-prepared KNbO3 samples was evaluated regarding the hydrogen evolution from aqueous methanol under UV, and the results were compared with that of cubic KNbO3 microcubes. The photocatalytic reactivity was shown to be phase-dependent, following the order cubic > orthorhombic > tetragonal. Insight into the phase-dependent photocatalytic properties was gained by first-principles density functional calculations. The best photocatalytic performance of cubic KNbO3 is ascribed to it having the highest symmetry in the bulk structure and associated unique electronic structure. Further, the surface electronic structure plays a key role leading to the discrepancy in photoreactivity between orthorhombic and tetragonal KNbO3. The results from this study are potentially applicable to a range of perovskite-type mixed metal oxides useful in water splitting as well as other areas of heterogeneous photocatalysis.
TL;DR: In this paper, a tetragonal hausmannite (Mn3O4) was synthesized by pulsed-spray evaporation chemical vapor deposition (PSE-CVD) at moderate temperatures.
Abstract: Tetragonal hausmannite (Mn3O4) was synthesized by pulsed-spray evaporation chemical vapor deposition (PSE-CVD) at moderate temperatures. The thermal properties of the obtained Mn3O4 thin films were evaluated with a newly developed in situ emission FTIR method. The performance of Mn3O4 grown on flexible stainless steel mesh substrates was investigated toward the oxidation of CO and C3H6. X-ray diffraction (XRD) patterns, FTIR, and Raman spectroscopy reveal that only the single-phase tetragonal Mn3O4 spinel structure was obtained within the temperature range of 350–500 °C. The as-deposited Mn3O4 is thermally stable up to 800 °C, and its reduction plays a determinant role in the catalytic process. Compared to conventional powder catalysts, the combination of PSE-CVD, in situ emission FTIR, and the flexible substrate provides a novel tool for catalyst synthesis and the evaluation of the thermal properties and catalytic performance.
TL;DR: The ability to control materials properties through interface engineering is demonstrated by the appearance of conductivity at the interface of certain insulators, most famously the {001} interface of the band insulators LaAlO${3}$ and TiO$_{2}$-terminated SrTiO$³$ (STO) as discussed by the authors.
Abstract: The ability to control materials properties through interface engineering is demonstrated by the appearance of conductivity at the interface of certain insulators, most famously the {001} interface of the band insulators LaAlO$_{3}$ and TiO$_{2}$-terminated SrTiO$_{3}$ (STO). Transport and other measurements in this system show a plethora of diverse physical phenomena. To better understand the interface conductivity, we used scanning superconducting quantum interference device microscopy to image the magnetic field locally generated by current in an interface. At low temperature, we found that the current flowed in conductive narrow paths oriented along the crystallographic axes, embedded in a less conductive background. The configuration of these paths changed on thermal cycling above the STO cubic-to-tetragonal structural transition temperature, implying that the local conductivity is strongly modified by the STO tetragonal domain structure. The interplay between substrate domains and the interface provides an additional mechanism for understanding and controlling the behaviour of heterostructures.
TL;DR: Yttrium-doped BiVO4 has been synthesized by means of a surfactant free hydrothermal method having good photoactivities under sun-like excitation for the degradation of Methylene Blue (MB).
Abstract: Yttrium-doped BiVO4 has been synthesized by means of a surfactant free hydrothermal method having good photoactivities under sun-like excitation for the degradation of Methylene Blue (MB). From the...
TL;DR: In this article, a phase field model was developed to account for the main metallurgical mechanisms governing the tetragonal-to-monoclinic transition in zirconia, where the symmetry reduction and orientation relationship between the parent and product phases were simulated using several nonconserved order parameters representing different transformation paths.
TL;DR: In this paper, tetragonal ZrO2 nanoparticles and nanosheets were synthesized with citric acid assisted sol-gel method, and the effects of heat treatment on zirconia phase evolution were investigated.
TL;DR: In this article, X-ray diffraction and Raman spectroscopy reveals that all the ferrite samples are in single-phase with tetragonal structure for CFO and cubic spinel structure for CMFO samples.
TL;DR: In this paper, high-energy synchrotron X-ray diffraction was used to characterize the oxides formed by autoclave exposure on Zr-Sn-Nb alloys with tin concentration ranging from 0.01 to 0.92.
TL;DR: The preliminary investigation indicates that Cs2GeB4O9 is a new promising second-order nonlinear-optical crystalline material that possesses a short-wavelength absorption edge onset determined by UV-vis transmission spectroscopy measurements on a slab of polished crystal.
Abstract: A new alkali-metal borogermanate with noncentrosymmetric structure, namely, Cs2GeB4O9, has been discovered, and a large crystal with dimensions of 20 × 16 × 8 mm3 has been grown by a high-temperature top-seeded solution method using Cs2O–B2O3 as a flux. The compound crystallizes in the tetragonal space group I4 with a = b = 6.8063(2) A, c = 9.9523(7) A, V = 461.05(4) A3, and Z = 2. It features a three-dimensional anionic open framework based on GeO4 tetrahedra and B4O9 clusters that are interconnected via corner-sharing, forming one-dimensional channels of nine-/ten-membered rings along the a and b axes, which are occupied by Cs+ cations. Cs2GeB4O9 exhibits a very high thermal stability with a melting point of 849 °C, and it possesses a short-wavelength absorption edge onset at 198 nm determined by UV–vis transmission spectroscopy measurements on a slab of polished crystal. Powder second-harmonic generation (SHG) measurement on sieved crystals reveals that Cs2GeB4O9 is a type I phase-matchable material w...
TL;DR: In this article, the average particle size and the surface areas play an important role in effecting the lithium-ion storage capability and cycling ability, and the existence of metastable FexCu1−x alloy in the discharged nanocomposition for the first time, which exhibits the interaction of metallic Cu particles with the adjacent iron ions.
TL;DR: In this paper, the Li+ ion conductor Li7La3Zr2O12 was synthesized by solid state reaction as a ceramic with tetragonal and cubic crystal structure.
TL;DR: It is suggested that Li diffusion in this record solid electrolyte is less anisotropic than previously claimed.
Abstract: Tetragonal Li10GeP2S12 (LGPS) is the best solid Li ion conductor known to date. So far, the structure of the electrolyte was only determined from powder diffraction and Rietveld refinement. Here, we present the first single-crystal structure analysis of the tetragonal LGPS structure. The reported structure is largely verified. However, an additional Li position is clearly identified which might have a significant impact on the Li ion dynamics. All Li positions are partially occupied – a prerequisite for Li superionic conductors – and form a network of interconnected Li diffusion pathways. Therefore, we suggest that Li diffusion in this record solid electrolyte is less anisotropic than previously claimed.
TL;DR: In this article, a lead-free piezoelectric system based on (1−x)KNNS-xBNKLZ is developed, and a rhombohedral-tetragonal phase boundary is constructed in this system.
Abstract: In this work, a lead-free piezoelectric system based on (1−x)(K0.48Na0.52)(Nb0.95Sb0.05)O3-xBi0.5(Na0.7K0.2Li0.1)0.5ZrO3 [(1−x)KNNS-xBNKLZ] is developed, and a rhombohedral-tetragonal phase boundary is constructed in this system. The relationship between the phase boundary and the piezoelectric properties of the (1−x)KNNS-xBNKLZ ceramics is illuminated. The coexistence of a tetragonal phase and a rhombohedral phase is identified in the composition range of 0.03 300 pC/N) of ∼210 °C. We believe that the (1−x)KNNS-xBNKLZ system is very promising for lead-free piezoelectric applications.
TL;DR: In this paper, a 3D hierarchical structure of β-Bi2O3 microspheres with high specific surface area and excellent visible-light-driven photocatalytic activity for degradation of Rhodamine B was successfully synthesized via a facile hydrothermal process and subsequent calcination.
Abstract: Flower-like β-Bi2O3 microspheres with high specific surface area and excellent visible-light-driven photocatalytic activity (for degradation of Rhodamine B) were successfully synthesized via a facile hydrothermal process and subsequent calcination. By precisely adjusting the hydrothermal conditions, the composition and morphology of the microspherical precursors could be well controlled, so that upon further optimized calcination of the precursors, the selective formation of the monoclinic α-Bi2O3 and tetragonal β-Bi2O3 with three dimensional (3D) hierarchical architectures could be achieved. These tetragonal β-Bi2O3 microspheres with an average diameter of 3 μm were constructed by nanoflakes with an average thickness of 50 nm, which, as far as we know, is the first reported result on the 3D hierarchical architectures of tetragonal β-Bi2O3. Its flower-like microspherical architecture made the tetragonal β-Bi2O3 possess not only much improved specific surface area but also a narrower band gap, which significantly enhanced its visible-light-driven photocatalytic activity for the degradation of Rhodamine B (RhB). To further optimize the synthetic conditions and realize the controllable synthesis, the formation mechanism for the morphologies and polymorphs of the Bi2O3 microspheres was discussed in detail.
TL;DR: In this paper, a combination of rhombohedral R3m and tetragonal P4mm is found to coexist at temperatures of 20°C and −25°C.
Abstract: The solid solution of (x)Ba0.7Ca0.3TiO3-(1-x)BaZr0.2Ti0.8O3 is known to exhibit high piezoelectric constants. Discrepancies in the reported phase transitions and structure around room temperature, however, have complicated the understanding of the enhanced properties. Rietveld refinement of high-resolution X-ray diffraction is employed here to establish and refine the crystallographic structure at temperatures from −100 °C to 150 °C for x = 0.5. A combination of rhombohedral R3m and tetragonal P4mm is found to coexist at temperatures of 20 °C and −25 °C, bordered by single phase rhombohedral and tetragonal regions at lower (i.e., −100 °C) and higher (i.e., 70 °C) temperatures, respectively. The diffractograms also show signs of strain and domain wall scattering that are linked to the sample history.
TL;DR: In this article, a detailed residual stress and phase fraction analysis was carried out for the oxides formed on Zircaloy-4 after autoclave exposure at 360°C for various times by means of synchrotron X-ray diffraction.