Study of the structure and lattice vibrations of Ce6Rh30Si19 and A6Pt30Si19 (A = Th, U)

We present an atomistic study on the phase stability, site preference and lattice constants of the rare earth or actinium intermetallics Ce₆Rh₃₀Si₁₉ and A₆Pt₃₀Si₁₉ (A = Th, U). The calculated preferential occupation site of one Si atom is found to be the 2b site in Ce₆Rh₃₀Si₁₉ and A₆Pt₃₀Si₁₉. The Si atom is located at the sites 2b with occupancy close to 50%. Our calculated lattice constants agree with a report in the literature. The total and partial phonon densities of states are evaluated first for these complicated defect structures. The analysis of the inverted potentials explains qualitatively the contributions of different atoms to the vibrational modes.     

Effect of lattice matching on microstructure and electrical conductivity of epitaxial ARuO3 (A = Sr, Ca and Ba) thin films prepared on (001) LaAlO3 substrates by laser ablation

(001) SrRuO₃ (SRO), (001) CaRuO₃ (CRO) and (205) BaRuO₃ (BRO) thin films were epitaxially grown on (001) LaAlO₃ substrates by laser ablation, and the effect of lattice matching on the microstructure and electrical conductivity was investigated. (001) SRO and (001) CRO thin films had a terrace with orthogonal step structure, whereas (205) BRO thin film had an orthogonal structure with tetragonal grains. Epitaxial thin films showed metallic conduction, and the (001) CRO thin films exhibited the highest electrical conductivity, i.e. 1.5 × 10⁵ S m^− 1, among the (001) SRO, (001) CRO and (205) BRO thin films. The smaller misfit between thin film and substrate could be associated with the higher electrical conductivity.     

Formation of local magnetic moments in (V,Ti)3S4

The system of V_1?xTi_xS_1.40 has been studied through magnetic susceptibility and NMR measurements. The Curie constant increases with quadratic dependence on the composition x within the V₃S₄ phase (0 ≤ x ≤ 0.6) and then, rapidly decreases toward the Ti₂S₃ phase (0.8 < x ≤ 1.0). The NMR absorption from V⁵¹ nuclei with itinerant delectrons rapidly decreases with increasing Ti content in the former phase. These phenomena may indicate that local magnetic moments are formed in this system under a particular environment of vanadium atoms proposed. Metal distribution of V and Ti is also discussed.     

Hydrothermal synthesis, structural and physico-chemical characterizations of two Nasicon phosphates: M0.50Ti2(PO4)3 (M = Mn, Co)

The family of titanium Nasicon-phosphates of generic formula M_0.5^IITi₂(PO₄)₃ has been revisited using hydrothermal techniques. Two phases have been synthesized: Mn_0.5^IITi₂(PO₄)₃ (MnTiP) and Co_0.5^IITi₂(PO₄)₃ (CoTiP). Single crystal diffraction studies show that they exhibit two different structural types. Mn_0.5^IITi₂(PO₄)₃ phosphate crystallizes in the R-3 space group, with the cell parameters a = 8.51300(10) Å and c = 21.0083(3) Å (V = 1318.52(3) Å³ and Z = 6). The Co_0.5^IITi₂(PO₄)₃ phosphate crystallizes in the R-3c space group, with a = 8.4608(9) Å and c = 21.174(2) Å (V = 1312.7(2) Å³ and Z = 6). These two compounds are clearly related to the parent Nasicon-type rhombohedral structure, which can be described using [Ti₂(PO₄)₃] framework composed of two [TiO₆] octahedral interlinked via three [PO₄] tetrahedra. ³¹P magic-angle spinning nuclear magnetic resonance (MAS-NMR) data are presented as supporting data. Curie-Weiss-type behavior is observed in the magnetic susceptibility. The phases are also characterized by IR spectroscopy and UV-visible.     

Ge、Si元素对ZrO2和Zr(Fe,Cr)2能量与电子结构的影响

采用基于密度泛函理论的第一性原理计算方法,研究Ge、Si元素对锆合金中与腐蚀相关的ZrO_2氧化膜相和Zr(Fe,Cr)_2第二相能量与电子结构的影响。合金形成热、结合能的计算结果表明:ZrO_2四方相结构不稳定,立方相易形成且结构稳定,氧化膜晶体结构从四方相向立方相发生转变影响锆合金的耐腐蚀性能;Ge、Si元素均降低ZrO_2立方相的结构稳定性和形成能力,与Ge相比,Si易取代Zr(Fe,Cr)_2第二相中的Cr,增加锆合金Fe/Cr原子比。电子态密度和Mulliken电子占据数的计算结果表明:ZrO_2中Zr与O存在杂化共振与较强的离子键作用,Ge、Si降低ZrO_2立方相结构稳定性的原因主要在于削弱了Zr-O之间的离子键作用;ZrO_2氧化膜相和Zr(Fe,Cr)_2第二相是影响锆合金耐腐蚀性能的两个重要因素,对Si而言,形成含Si的Zr(Fe,Cr)_2第二相对锆合金耐腐蚀性能产生不利影响,改善锆合金耐腐蚀性能需要ZrO_2晶体结构改变占主导地位;对Ge而言,含Ge的Zr(Fe,Cr)_2第二相难形成,第二相对锆合金耐腐蚀性能的影响相对Si较小,减缓ZrO_2由四方相向立方相的转变倾向,是Ge改善锆合金耐腐蚀性能的重要原因。     

Synthesis and crystal structure of new U(VI) and Np(VI) benzoates, K11(AnO2)23(OOCC6H5)57(H2O)18+x

The structure of new double benzoates of hexavalent actinides, K₁₁(AnO₂)₂₃(O₂C₇H₅)₅₇(H₂O)_18+x (An = U, Np), was studied. There are five crystallographically independent actinide atoms in the crystals. The coordination polyhedra of An(1), An(3), An(4), and An(5) are distorted hexagonal bipyramids, and that of An(2) is a distorted pentagonal bipyramid. Ten crystallographically independent benzoate ions have been found in the crystals. All but one anions are bidentate chelating and form with AnO₂²⁺ cations either electrically neutral [AnO₂(O₂C₇H₅)₂(H₂O)₂][An(1)O₂²⁺ cations] or negatively charged [AnO₂(O₂C₇H₅)₃]⁻[An(3)O₂²⁺, An(4)O₂²⁺, An(5)O₂²⁺ cations] complexes. The bidentate bridging benzoate ion links two adjacent An(2)O₂²⁺ cations with the formation of peculiar electrically neutral cyclic fragments [AnO₂(O₂C₇H₅)₂(H₂O)]₆ arranged perpendicular to the c-axis. There are three independent K⁺ cations in the structure. The coordination surrounding of K(1)⁺ (coordination number CN 6) is formed by oxygen atoms of two electrically neutral [AnO₂(O₂C₇H₅)₂(H₂O)₂] fragments and of the complex anion [AnO₂(O₂C₇H₅)₃]⁻. The coordination surrounding of K(2)⁺ (CN 6) consists of oxygen atoms of three complex anions [AnO₂(O₂C₇H₅)₃]⁻. The disordered K(3)⁺ cation is arranged near the sixfold axis between the cyclic fragments [AnO₂(O₂C₇H₅)₂(H₂O)]₆. An important structure-forming factor in the crystals is hydrogen bonding involving coordinated water molecules. In the coordination polyhedra of actinides, the An-O bond lengths regularly decrease in going from U to Np owing to actinide contraction.     

Medium-entropy(Me,Ti)0.1(Zr,Hf,Ce)0.9O2(Me = Y and Ta): Promising thermal barrier materials for high-temperature thermal radiation shielding and CMAS blocking

With continuous enhancement of gas-turbine inlet temperature and rapid increase of radiant heat transfer,thermal barrier coating(TBC) materials with a combination of low thermal conductivity and good high-temperature thermal radiation shielding performance play vital roles in ensuring the durability of metallic blades.However,yttria-stabilized zirconia(YSZ),as the state-of-the-art TBC and current industry standard,is unable to meet such demands since it is almost translucent to high-temperature ...     

Luminescence properties of Ca4Y6(SiO4)6O:RE (RE = Eu, Tb, Dy, Sm and Tm) under vacuum ultraviolet excitation

The vacuum ultraviolet excited luminescent properties of Eu³⁺, Tb³⁺, Dy³⁺, Sm³⁺ and Tm³⁺ in the matrices of Ca₄Y₆(SiO₄)₆O were investigated. The bands at about 173 nm in the vacuum ultraviolet excited spectra were attributed to host lattice absorption of the matrix Ca₄Y₆(SiO₄)₆O. For Eu³⁺-doped samples, the O²⁻ → Eu³⁺ CTB was identified at 258 nm. Typical 4f-5d absorption bands in the region of 195-300 nm were observed in Tb³⁺-doped samples. For Dy³⁺-doped and Sm³⁺-doped samples, the broad excitation bands consisted of host absorptions, CTB and f-d transition. For Tm³⁺-doped samples, the O²⁻ → Tm³⁺ CTB was located at 191 nm. About the color purity and emission intensity, Ca₄Y₆(SiO₄)₆O:Tb³⁺ is an attractive candidate of green light PDP phosphor, and Ca₄Y₆(SiO₄)₆O:Dy³⁺ has potential application in the field of mercury-free lamps.     

Synthesis of New Crystalline Pu(V) Compounds from Solutions: IV. Double Pu(V) Malonates of the Composition Co(NH3)6[PuO2C3H2O4]2A ? nH2O, A = NO3, ClO4, Cl, and Br

New crystalline compounds of the composition Co(NH₃)₆[PuO₂L]₂A ⋅ nH₂O, where L = C₃H₂O₄ and A = NO₃, ClO₄, Cl, and Br, were obtained by addition of a small excess of Co(NH₃) ₆ ³⁺ ions to freshly prepared neutral malonate solutions of Pu(V). They are fairly stable in storage in air and isostructural to the corresponding Np(V) compounds. Thermal behavior of the compounds synthesized was studied, and their IR spectra were measured.__________Translated from Radiokhimiya, Vol. 47, No. 3, 2005, pp. 224–227.Original Russian Text Copyright © 2005 by Krot, Bessonov, Charushnikova, Grigor’ev, Makarenkov.     

Residual stress development in Pb(Zr,Ti)O3/ZrO2/SiO2 stacks for piezoelectric microactuators

The residual stress of multilayers in piezoelectric microelectromechanical systems structures influences their electromechanical properties and performance. This paper describes the development of residual stress in 1.6 μm Pb(Zr_0.52,Ti_0.48)O₃ (PZT)/0.3 μm ZrO₂/0.5 μm SiO₂ stacks for microactuator applications. The residual stresses were characterized by wafer curvature or load-deflection measurements. PZT and zirconia films were deposited on 4-in. (100) silicon wafers with 0.5 μm thick thermally grown SiO₂ by sol–gel processes. After the final film deposition, the obtained residual stress of PZT, ZrO₂, and SiO₂ were 100–150, 230–270, and − 147 MPa, respectively. The average stress in the stack was  80 MPa. These residual stresses are explained in terms of the thermal expansion mismatch between the layers and the substrate. Load-deflection measurements were conducted to evaluate localized residual stresses using released circular diaphragms. The load-deflection results were consistent with the average stress value from the wafer curvature measurements. It was found that more reasonable estimates of the stack stresses could be obtained when mid-point vertical deflection data below 6 μm were used, for diaphragms 0.8–1.375 mm in diameter.     

Nanopowders of YAl3(BO3)4 doped by Nd, Yb and Cr obtained by sol-gel method: Synthesis, structure and luminescence properties

Structure, morphology and luminescence properties of nanocrystalline samples of YAl₃(BO₃)₄ (YAB) undoped and doped with neodymium, ytterbium and chromium obtained by the sol-gel method are presented. The best results of synthesis are obtained for mannitol as polymerizing agent. Single phase of nanopowder is obtained for pure YAB. Dopants destroy the compound structure; two other compounds, namely Al₁₈B₄O₃₃ and YBO₃, were revealed by X-ray investigation. Nanopowders show isometric and needles forms, the calculated size of crystallites is about 60 nm. Their optical properties are determined and results are compared to data obtained for single crystal counterparts. It is shown that the influence of rare earth ions incorporated into YBO₃ phase on luminescent spectra and excited state relaxation dynamics of the nanopowders is negligibly small when the YBO₃ content is of the order of several wt%. Residual impurity phases do not affect significantly spectroscopic properties of YAB nanopowders.     

Structural and thermochemical properties, and energetics of C8(NO2)8 and C20(NO2)4n (n = 0–4)

Density-functional-theory calculations, at the B3LYP level with the 6–31 G basis set, have been performed to investigate the structural and electronic properties of octanitrocubane, C₈(NO₂)₈, and polynitrofullerenes of type C₂₀(NO₂)_4n, with n = 0–4, in their ground states. Having determined their energetically optimized geometric structures, energetics, and vibrational frequencies, we have calculated the enthalpies of combustion and decomposition of these molecules. Extrapolating from the so-obtained data, we have also estimated, as a by-product, the enthalpy values of C₂₀(NO₂)₂₀.     

Band bending at free Pb(Zr,Ti)O3 surfaces analyzed by X-ray photoelectron spectroscopy

This paper analyses in detail the core levels evolution of Pb(Zr,Ti)O₃, i.e. Pb 4f, Zr 3d, Ti 2p, O 1s in various conditions: absolutely freshly prepared sample, sample stored under air, and the effects of in vacuum annealing. The aim of the study is to quantify separately the chemical reactivity at the surface and the band bending effects due to the ferroelectric polarization. It is found that freshly prepared samples present mostly inwards (↓) polarization. This phenomenon is mostly revealed by the Ti 2p and O 1s spectra, manifested as a distinct component with 1.8 eV lower binding energy in the O 1s binding energy and by 1.1 eV in the Ti 2p binding energy. Sample aging under air suppresses the inwards polarization, and most signal comes from surfaces not presenting ferroelectric permanent polarization perpendicular to the sample surface. This process conducts also to the formation of Pb(CO₃)₂ on the surface. Annealing to temperatures up to 400 °C stabilizes a surface composed by a main part of surface without polarization perpendicular to the surface, and with some areas presenting outwards (↑) polarization. These areas have, most probably, different terminations, the polarized area being (Ti,Zr)O₂ terminated.     

Dielectric and electric studies of the [N(CH3)4][N(C2H5)4]ZnCl4 compound at low temperature

The [N(CH₃)₄][N(C₂H₅)₄]ZnCl₄ compound was prepared and characterized by electrical technique. The temperature dependence of the dielectric permittivity shows that this compound is ferroelectric below T = 268 K. The two semi-circles observed in the complex impedance identify the presence of the grain interior and grain boundary contributions to the electrical response in the material. The equivalent circuit is modeled by a combination series of two parallel R_P–CPE circuits. The frequency dependent conductivity is interpreted in term of Jonscher's law. The modulus plots can be characterized by the empirical Kohlrausch–Williams–Watts (K.W.W.) function: ?(t) = exp [(−t/τ)^β]. The temperature dependence of the alternative current conductivity (σ_p), direct current conductivity (σ_dc) and the relaxation frequency (f_p) confirm the presence of the ferroelectric–paraelectric phase transition.     

Inorganic phosphate crystal Na15−n[Al(PO4)2F2]3−n[Ti(PO4)2F2]n (0 ≤ n < 1): A novel cation exchanger with high exchange selectivity for Li and Pb ions

A series of inorganic phosphate crystals have been hydrothermally synthesized, which have high chemical stability and can keep their crystal structure after acid/base treatments. Its cation-exchange properties have been investigated and the results show that it is an excellent ion exchanger with high exchange capacities for H⁺, Li⁺ and Pb²⁺ ions (12.74, 6.98 and 3.92 mequiv./g, respectively). Selective extractions of Li⁺ and Pb²⁺ from the synthetic mixtures containing (Li⁺, Sr⁺, K⁺, Mg²⁺, Ca²⁺ and Ba²⁺) and (Pb²⁺, Ca²⁺, Ba²⁺, Co²⁺, Ni²⁺, Zn²⁺ and Mg²⁺) have been observed. The reasons of the high exchange selection of NATP for Li⁺ and Pb²⁺ ions have been discussed.     

Structural and vibrational properties of microcrystalline TlM(MoO4)2 (M = Nd, Pr) molybdates

The microcrystalline TlNd(MoO₄)₂ and TlPr(MoO₄)₂ molybdates have been prepared with solid state synthesis on the same synthesis route. The final products have been studied by XRD and SEM. Vibrational properties have been evaluated with Raman spectroscopy. More than 20 narrow Raman lines have been observed in the experimental spectrum of the microcrystals. The most intensive lines related to breathing vibrations of MoO₄ tetrahedra have been found at 904 and ∼930 cm⁻¹. The earlier proposed empirical relation between MoO bond length and stretching mode wavenumber has been tested by the comparative analysis for a suite of sixteen complex molybdates. This well-known relation is found to be unusable for molybdates containing different cations in the crystal lattice.     

Structural characterization, thermal, spectroscopic and magnetic studies of the (C3H12N2)0.75[Mn1.50Fe1.50(AsO4)F6] and (C3H12N2)0.75[Co1.50Fe1.50(AsO4)F6] compounds

The (C₃H₁₂N₂)_0.94[Mn_1.50Fe_1.50^III(AsO₄)F₆] and (C₃H₁₂N₂)_0.75[Co_1.50Fe_1.50^III(AsO₄)F₆] compounds 1 and 2 have been synthesized using mild hydrothermal conditions. These phases are isostructural with (C₃H₁₂N₂)_0.75[Fe_1.5^IIFe_1.5^III(AsO₄)F₆]. The compounds crystallize in the orthorhombic Imam space group. The unit cell parameters calculated by using the patterns matching routine of the FULPROOF program, starting from the cell parameters of the iron(II),(III) phase, are: a = 7.727(1) Å, b = 11.047(1) Å, c = 13.412(1) Å for 1 and a = 7.560(1) Å, b = 11.012(1) Å, c = 13.206(1) Å for 2, being Z = 8 in both compounds. The crystal structure consists of a three-dimensional framework constructed from edge-sharing [M^II(1)₂O₂F₈] (M = Mn, Co) dimeric octahedra linked to [Fe^III(2)O₂F₄] octahedra through the F(1) anions and to the [AsO₄] tetrahedra by the O(1) vertex. This network gives rise two kinds of chains, which are extended in perpendicular directions. Chain 1 is extended along the a-axis and chain 2 runs along the c-axis. These chains are linked by the F(1) and O(1) atoms and establish cavities delimited by eight or six polyhedra along the [1 0 0] and [0 0 1] directions, respectively. The propanediammonium cations are located inside these cavities. The thermal study indicates that the structures collapse with the calcination of the organic dication at 255 and 285 °C for 1 and 2, respectively. The Mössbauer spectra in the paramagnetic state indicate the existence of two crystallographically independent positions for the iron(III) cations and a small proportion of this cation in the positions of the divalent Mn(II) and Co(II) ones. The IR spectrum shows the protonated bands of the H₂N- groups of the propanediamine molecule and the characteristic bands of the [AsO₄]³⁻ arsenate oxoanions. In the diffuse reflectance spectra, it can be observed the bands characteristic of trivalent iron(III) cation and divalent Mn(II) and Co(II) ones in a distorted octahedral symmetry. The calculated Dq and B-Racah parameters for the cobalt(II) phase are 710 and 925 cm⁻¹, respectively. The ESR spectra of compound 1 maintain isotropic with variation in temperature, being g = 1.99. Magnetic measurements for both compounds indicate that the main magnetic interactions are antiferromagnetic in nature. However, at low temperatures small ferromagnetic components are detected, which are probably due to a spin decompensation of the two different metallic cations. The hysteresis loops give values of the remnant magnetization and coercive field of 84.5, 255 emu/mol and 0.01, 0.225 T for phases 1 and 2, respectively.     

Vacuum-ultraviolet ellipsometry spectra and structural properties of Pb(Zr,Ti)O3 films

Optical properties of PbZr_xTi_1 − xO₃ material have been actively studied in the visible and near band-gap region, but data in the vacuum-ultraviolet spectral region is rather scarce. In this work we focus on well known interband transitions for the perovskite materials, 2p → dγ, located in VUV spectral region. Dielectric functions of chemical solution deposited and sputtered PZT were obtained in the spectral range 1-8.8 eV. Differences between the absorption maxima for chemical solution deposited and sputtered PbZr_xTi_1 − xO₃ samples near Kahn-Leyendecker 2p → dγ interband transition were found and are interpreted by change of interatomic distances. This is confirmed by different lattice constants. In the case of PbZr_xTi_1 − xO₃ film with microcracks, the void fraction was estimated from the effective medium approximation. Direct band-gap energies appear to be nearly the same for all reactive sputtered samples weakly depending of Zr/Ti concentration.     

A thermodynamic study of the systems Tiox (X=Cl2, SeCl4 OR HCl) I. Investigation of the systems TiO2cl2, TiO2seC14 and TiO2tihCl (TiO2 : Ti = 1 : 1)

The equilibrium composition of the gaseous phase and the yield of titanium oxides in the systems TiO₂cl₂, TiO₂seCl₄, TiO₂hCl and TiO₂tihcl (TiO₂ : Ti = 1 : 1) have been calculated with different preset values of temperature, total pressure and oxygen/halogen derivative ratio. In the systems with Cl₂ and SeCl₄ the presence of only one oxide phase of titanium, TiO₂, was established, its amount being higher in the case of chlorine. In the TiO₂-HCl system, Ti₃O₅ was found in the condensed phase along with the prevailing amount of TiO₂. The percentage of Ti₃O₅ increased with the increase in temperature and initial concentration of HCl. It is shown that in the TiO₂-Ti-HCl system the solid phase obtained should be TiO with a Ti₂O₃ admixture in an amount depending on the total pressure.