Electronic Structure of Oxygen Vacancies in the Orthorhombic Noncentrosymmetric Phase Hf<Subscript>0.5</Subscript>Zr<Subscript>0.5</Subscript>O<Subscript>2</Subscript>

The electronic structure of stoichiometric and oxygen-depleted Hf_0.5Zr_0.5O₂ in the orthorhombic noncentrosymmetric phase has been studied by X-ray photoelectron spectroscopy and quantum-chemical simulation based on the density functional theory. It has been established that the ion-etching-induced peak in the photoelectron emission spectrum with the energy above the top of the o-Hf_0.5Zr_0.5O₂ valence band is due to oxygen vacancies. A method of estimating the density of oxygen vacancies from the comparison of the experimental and theoretical photoelectron spectra of the valence band has been proposed. It has been established that oxygen polyvacancies in o-Hf_0.5Zr_0.5O₂ are not formed: the energetically favorable spatial arrangement of oxygen vacancies in a crystal corresponds to noninteracting oxygen vacancies distant from each other.     

Short-Range Order in Amorphous and Crystalline Ferroelectric Hf<Subscript>0.5</Subscript>Zr<Subscript>0.5</Subscript>O<Subscript>2</Subscript>

The microstructures of amorphous and polycrystalline ferroelectric Hf_0.5Zr_0.5O₂ films are studied by X-ray spectroscopy and ellipsometry. EXAFS spectra demonstrate that the amorphous film consists of an “incompletely mixed” solid solution of metallic oxides HfO₂ and ZrO₂. After rapid thermal annealing, the mixed Hf_0.5Zr_0.5O₂ oxide films have a more ordered polycrystalline structure, and individual Hf and Zr monoxide islands are formed in the films. These islands are several nanometers in size and have a structure that is similar to the monoclinic structure of HfO₂ and ZrO₂. The presence of the HfO₂ and ZrO₂ phases in the Hf_0.5Zr_0.5O₂ films is also detected by ellipsometry.     

Dynamic analysis of non-linear wake-up behavior in Hf0.7Zr0.3O2 thin film

We report on the nonlinear wake-up behavior against the external electric field cycling in the ferroelectric Hf_0.7Zr_0.3O₂ thin film. Two distinct scaling regimes during the increase of the remnant polarization with different activation energies were observed in TiN/Hf_0.7Zr_0.3O₂/TiN cells. The transmission electron microscopy revealed the structural phase transition from the monoclinic structure to the orthorhombic structure of the Hf_0.7Zr_0.3O₂ film after the wake-up behavior. During the phase change, as the remnant polarization enhanced, the dielectric constant of the Hf_0.7Zr_0.3O₂ film increased with the external field cycling. The temperature dependence of the wake-up behavior revealed that each estimated activation energies for the early and later enhancement of the remnant polarization are 1.12 eV and 0.73 eV, respectively. First principle calculations show that the oxygen vacancies can reduce the activation energy barrier for the structural phase transition.     

Ta对C—15相V2Hf和V2(Zr0.5Hf0.5)系列声子性能的影响

本文用中子飞行时间方法对C-15相的超导材料V₂Hf,V₂Ta和V₂Hf_0.8Ta_0.2以及V₂Zr_0.5。Hf_0.5和V₂Zr_0.5Hf_0.33Ta_0.17的热中子非弹性散射谱作了测量,并计算出相对的广义声子态密度。结果与早先发表的Nb对C-15相V₂Zr和V₂(Hf_0.5Zr_0.5)系列声子性能的影响一致:声子频率随超导转变温度T_c增加而软化,随T_c减小而硬化。这表明,对于此类材料弹性软化在一定程度上对提高T_c起了作用。结果还进一步表明V₂Zr或V₂Hf与V₂(Zr_0.5Hf_0.5)之间有着质的差别,V₂Hf加Ta后,T_c增加,声子频率软化,而V₂(Zr_0.5Hf_0.5)加Ta后,T_c减小,声子频率则略有硬化。这与V₂Zr和V₂(Hf_0.5Zr_0.5)加Nb的结果是一致的。此结果可以用角动量分波表象的能带论方法分析电-声耦合相互作用得出的杂化理论来定性解释。 关键词：     

Preparation and electrical properties of a pyrochlore-related Ce2Zr2O8−x phase

A pyrochlore-related Ce₂Zr₂O_8−x phase has been prepared in a reduction reoxidation process from Ce_0.5Zr_0.5O₂ powders. Ce₂Zr₂O_8−x, based on a cubic symmetry with a=1.053 nm, decomposes in nitrogen at 800 °C, but remains stable up to 900 °C in air. It shows mixed oxygen ionic and electronic conductivity. The bulk conductivity at 700 °C is 4×10⁻⁴ S cm⁻¹ in air and 1×10⁻² S cm⁻¹ in nitrogen, and the activation energy is 1.27 eV in air. In nitrogen, the Arrhenius law is not obeyed, and a curved plot was obtained from 400 to 700 °C; then, the conductivity decreased rapidly due to the thermal decomposition of Ce₂Zr₂O_8−x.     

Effect of the annealing temperature of thin Hf0.3Zr0.7O2 films on their energy storage behavior

With increasing annealing temperature (T_anneal), the magnitude of the electric fields for the antiferroelectric‐to‐ferro‐electric (E_AF) and ferroelectric‐to‐antiferroelectric (E_FA) transition of a 9.2 nm thick Hf_0.3Zr_0.7O₂ film decreased. The energy storage densities of the Hf_0.3Zr_0.7O₂ films crystallized at 400 °C, 500 °C, and 600 °C were as large as 42.2 J/cm³, 40.4 J/cm³, and 28.3 J/cm³, respectively, at the electric field of 4.35 MV/cm. The maximum dielectric constant of the Hf_0.3Zr_0.7O₂ film crystallized at 600 °C was the largest (～46) as it had the smallest E_AF and E_FA, whereas the leakage current density of the film crystallized at 400 °C was the smallest. The 400 °C of T_anneal was the optimum condition for energy storage application. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

(Hf0.5Zr0.5V2)Hx的声子谱与超导性的关系

本文报道了用Be过滤探测器谱仪对C-15相的(Hf_0.5Zr_0.5V₂₎H_x等五种样品的声子谱的测量。观察到了它们的声子谱随含氢量而变化以及声学支有规则的软化现象。表明(Hf_0.5Zr_0.5V₂₎H_x的T_c随x的变化,主要是声学支的贡献,声学文软化有利于T_c的提高,而光学支“软化”可能会抑制超导性。 关键词：     

Dielectric properties and electrical conduction of La2O3-doped (Bi0.5Na0.5)0.94Ba0.06TiO3 ceramics

La₂O₃ (2 wt%)-doped (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ (abbreviated as BNBT6) lead-free piezoelectric ceramics were synthesized by conventional solid-state reaction. X-ray diffraction (XRD) patterns indicated that La₂O₃ has diffused into the lattice of BNBT6 ceramics and formed a solid solution with a pure perovskite structure. Addition of La₂O₃ decreased the piezoelectric properties and electrical conductivity. It was used to study the electrical conductivity of the La₂O₃-doped BNBT6 lead-free piezoelectric ceramics combined with electrical modulus and impedance plots at the temperature range over 788–873 K. The values of activation energy derived from the electrical impedance and modulus were found to be 0.51 and 0.50 eV, respectively. The discrepancy between activation energy of relaxation frequency and the activation energy (0.25 eV) of dc electrical conductivity might have been due to a short-range migration or hopping of single ionized oxygen vacancy and a long-range migration or hopping of charge carriers over the whole disordered system, respectively.     

Nb对C-15结构V2(HfZr)系列的超导转变温度的影响

本文中研究了C-15结构V₂Hf_1-xNb_x,V₂Zr_1-xNb_x和V₂Hf_0.5Zr_0.5-xNb_x系列的超导转变温度T_c与Nb合量x的关系,发现V₂Zr,V₂Hf加Nb后与V₂Hf_0.5Zr_0.5加Nb后性能显著不同。测定了V₂Zr,V₂Hf和V₂Hf_0.5Zr_0.5的X射线光电子能谱。结果表明,当Hf原子和Zr原子共存于AB₂化合物的A位上时,发生了一种增强原子间相互作用的新的电荷转移。这个事实支持由角动量分波表象能带论方法分析电声耦合超导原理的结果对四元V₂(HfZrNb)系列的超导行为提出的一种可能解释:4d-5d原子配位可能有助于提高4d导带的杂化程度,从而有利于提高超导T_c。 关键词：     

Fast ionic conduction in cubic hafnium garnet Li<Subscript>7</Subscript>La<Subscript>3</Subscript>Hf<Subscript>2</Subscript>O<Subscript>12</Subscript>

A new member of the family of garnets with fast lithium ion conduction has been found with the composition Li₇La₃Hf₂O₁₂. The anion arrangement corresponds to the oxygen framework in garnets, e.g., in Ca₃Fe₂Si₃O₁₂. Hafnium is coordinated octahedrally while the lanthanum environment can be described as a distorted cube. Lithium occupies a large number of positions with tetrahedral, trigonal planar, and metaprismatic coordination. Li₇La₃Hf₂O₁₂ shows a lithium bulk ion conductivity of 2.4 × 10⁻⁴ Ω⁻¹ cm⁻¹ at room temperature with an activation energy of 0.29 eV.     

Nb对C-15相V2Zr和V2(HfZr)系列声子性能的影响

本文用中子飞行时间方法对C-15相的超导物质V₂Zr,V₂Zr_0.95Nb_0.05及V₂Hf_0.5Zr_0.5,V₂Hf_0.5Zr_0.3Nb_0.2的热中子非弹性散射谱作了测量,发现Nb的添加对V₂Zr和V₂Hf_{0.5 关键词：}     

Blue and red long lasting phosphorescence (LLP) in β-Zn3(PO4)2:Mn,Zr

Multi-color long lasting phosphorescent (LLP) phenomenon in β-Zn₃(PO₄)₂:Mn²⁺,Zr⁴⁺ was systematically investigated. It is found that the red (λ_Em=616 nm) LLP performance of Mn²⁺ such as brightness and duration is largely improved, and that the blue (λ_Em=475 nm) LLP of Zr⁴⁺ with lower intensity appears when Zr⁴⁺ ions are co-doped into the matrix. The fluorescence, phosphorescence and thermoluminescence (TL) spectra show that Mn²⁺ ion is solely expected as a luminescent center, while Zr⁴⁺ ion not only acts as a luminescent center, but also induces an electron trap (Trap_Zr) associated with a TL peak at 344 K. The trap depth for Trap_Zr is 0.25 eV, while that for the intrinsic trap is 0.38 eV, associated with a dominant peak at 385 K for Zn₃(PO₄)₂:Mn²⁺. The Zr⁴⁺-induced trap with suitable depth is responsible for the improvement of the red LLP of Mn²⁺ ion and the appearance of the blue LLP of Zr⁴⁺ ion. The LLP mechanism is also investigated.     

First-principle study of electronic structure and stability of Sn0.5Sb0.5O2

A theoretical study on Sb-doped SnO₂ has been carried out by means of periodic density functional theory (DFT) at generalized gradient approximation (GGA) level. Stability and conductivity analyses were performed based on the formation energy and electronic structures. The results show that Sn_0.5Sb_0.5O₂ solid solution is stable because the formation energy of Sn_0.5Sb_0.5O₂ is −0.06 eV. The calculated energy band structure and density of states showed that the band gap of SnO₂ narrowed due to the presence of the Sb impurity energy levels in the bottom of the conduction band, namely there is Sb 5s distribution of electronic states from the Fermi level to the bottom of conduction band after the doping of antimony. The studies provide a theoretical basis to the development and application of Sn_1−xSb_xO₂ solid solution electrode.     

Computer simulation of defects and oxygen transport in yttria-stabilized zirconia

We have used molecular dynamics simulations and energy minimization calculations to examine defect energetics and oxygen diffusion in yttria-stabilized zirconia (YSZ). Oxygen vacancies prefer to be second nearest neighbors to yttrium dopants. The oxygen diffusion coefficient shows a peak at 8 mol% yttria consistent with experimental findings. The activation energy for oxygen diffusion varies from 0.6 to 1.0 eV depending on the yttria content. The Y_Zr′–V_O^··–Y_Zr′ complex with a binding energy of − 0.85 eV may play an important role in any conductivity degradation of YSZ.     

Characterisation of the reduction properties of La0.5Sr0.5Fe0.5Co0.5O3

We report here on the characterisation by temperature programmed reduction, ⁵⁷Fe Mössbauer spectroscopy and X-ray absorption spectroscopy of the phases resulting from treatment of the perovskite-related material La_0.5Sr_0.5Fe_0.5Co_0.5O₃ in a flowing 90% hydrogen/10% nitrogen atmosphere. The results show that treatment of La_0.5Sr_0.5Fe_0.5Co_0.5O₃ (which contains approximately 50% Fe⁴⁺ and 50% Fe³⁺) in the flowing 90% hydrogen/10% nitrogen atmosphere at 600°C does not result in the reduction of any of the constituent elements of the material and that the perovskite structure is still retained. The Mössbauer spectrum recorded following heating in the gaseous reducing environment at 1,000°C shows the presence of metallic iron, an Fe³⁺-containing phase with parameters compatible with the presence of SrLaFeO₄ which has a K₂NiF₄-type structure, and a paramagnetic Fe³⁺ phase. The X-ray absorption spectroscopy results show the presence of metallic cobalt. The Mössbauer spectrum recorded following heating at 1,200°C continues to show the Fe³⁺-containing components plus a larger contribution from metallic iron. The X-ray absorption spectroscopy results show the presence of metallic cobalt, SrLaFeO₄, La₂O₃ and SrO.     

Solution of 111In impurities in the Hf(Zr)3Al2 minority phases of Hf(Zr)4Al3 samples

The hyperfine quadrupole interactions of ¹¹¹In/¹¹¹Cd probes in the polycrystalline isostructural Zr₄Al₃ and Hf₄Al₃ compounds were studied. Strong preference of ¹¹¹In solute for the Zr₃Al₂ and Hf₃Al₂ phases occurring as contaminant fractions in the measured samples was observed.     

Specific features of thermal phonon scattering and ferromagnetic properties of ZnO varistor ceramics

The scattering of thermal phonons (T = 2.3–3.8 K) in ZnO single crystals and related 97.5ZnO + 0.5Bi₂O₃ + 0.5Co₃O₄ + 0.5MnO₂ + 1Sb₂O₃ (mol %) ceramics has been studied. It is established that the transport characteristics of phonons with thermal frequencies in ceramics at liquid-helium temperatures are determined by the presence of Co²⁺ ions in ZnO grains. A model of phonon transport in ZnO-based ceramics is proposed that takes into account the electron states of cobalt. The energy of the corresponding level is estimated at Δ ≈ 5 K. Manifestations of the ferromagnetic effect are revealed.     

Electrochemical characterization of a lithiated mixed nickel-cobalt oxide (LiNi0.5Co0.5O2) prepared by sol-gel process

Lithiated transition metal oxides having a layered structure and general formula LiMO₂, have been extensively studied as positive electrode active materials for lithium or lithium-ion batteries. In particular, lithium nickel dioxide (LiNiO₂) and lithium cobalt dioxide (LiCoO₂) present a layered structure with high diffusion coefficients for the lithium ion. This latter property is very important in order to realize practical devices having high discharge rates. LiNiO₂, compared with LiCoO₂, has the advantage to be a cheaper material with a higher specific capacity for lithium cycling, but its stability upon cycling can be greatly influenced by the displacement of Ni ions from the Ni layers to the Li planes as the content in lithium is reduced over a certain value. Recently, solid solutions such as LiNi_xCo_1−xO₂ have been proposed to offer a compromise between stability, cost and capacity. In this work we have studied LiNi_0.5Co_0.5O₂ prepared by the Complex Sol-Gel Process (CSGP). The advantage of this procedure toward the solid-state process is the high homogeneity in composition and in particle dimension of the synthesized compounds. The samples have been characterized electrochemically using chronopotentiometric, voltammetric and impedance measurements in liquid electrolyte. The results indicates that CSGP-synthesized LiNi_0.5Co_0.5O₂ shows good cyclability (after 1000 cycles about 2/3 of the initial capacity can still be cycled) only if the anodic potential is limited to about 4.2 V. The quite low values of the specific capacity (∼70 mAh/g at C/1 charge-discharge rate) can be justified by the non-complete calcination reaction, as suggested by X-ray measurements. Kinetic properties have been evaluated by Electrochemical Impedance Spectroscopy measurements, which have shown quite high values for the lithium chemical diffusion coefficient (10⁻⁷÷10⁻⁸ cm²s⁻¹) and its unexpected decrease as deintercalation proceeds from x=0.5 in LiNi_0.5Co_0.5O₂. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997     

Optical properties of nanoscale BiFeO3/BaTiO3/Ni0.5Zn0.5Fe2O4 composite films obtained by the pulsed-laser deposition method

Nanoscale (30–100 nm) films of BiFeO₃/BaTiO₃/Ni_0.5Zn_0.5Fe₂O₄ complex composition have been obtained by the pulsed-laser deposition method. Optical properties of the films were studied in the wavelength range of 250–1000 nm. It is shown that the optical properties of amorphous films deposited at room temperature are explained by the Tauc model for amorphous semiconductors. An increase in the optical gap from 1.7 to 1.95 eV was observed with decreasing film thickness. Allowed direct-band transitions (E _g = 3.1 eV) were observed after annealing of films independent of their thickness.     

Dipole oscillator strengths for the photoabsorption,photoionization and fragmentation of molecular oxygen

The photoabsorption, photoionization and fragmentation of O₂ have been studied using electron impact coincidence methods to obtain branching ratios and dipole oscillator strengths (cross-sections). The photoabsorption measurements cover the energy range 5–300 eV while the formation of electronic states of O₂⁺ (photoelectron spectroscopy) and the resulting ionic fragmentation (photoionization mass spectrometry) are both measured from close to threshold up to photon energies of 75 eV. The binding energy spectra of O₂ show peaks at 33, 47 and 57 eV in addition to those reported elsewhere in the literature. These peaks are assigned to multiple final ion states arising from photoionization of the inner valence orbitals. Structure in the O₂⁺ electronic state partial oscillator strength curves is in good agreement with recent theoretical work which predicts the existence of several shape resonances. A quantitative picture of the dipole-induced breakdown of O₂ is obtained for the energy range 12–75 eV. The photoionization efficiency is found to be constant above 20 eV.