New high-pressure phase of HfTiO4 and ZrTiO4 ceramics

We studied the high-pressure effects on the crystalline structure of monoclinic HfTiO4 and ZrTiO4. We found that the compressibility of these ceramics is highly non-isotropic, being the b-axis the most compressible one. In addition, the a-axis is found to have a small and negative compressibility. At 2.7 GPa (10.7 GPa) we discovered the onset of an structural phase transition in HfTiO4 (ZrTiO4), coexisting the low- and high-pressure phases in a broad pressure range. The new high-pressure phase has a monoclinic structure which involves an increase in the Ti-O coordination and a collapse of the cell volume. The equation of state for the low-pressure phase is also determined.Comment: 16 pages, 5 figures, 26 references, Article in Pres

First-principles calculations of the electronic structure and mechanical properties of non-doped and Cr3+-Doped K2LiAlF6 under pressure

We report on the results of the first principles calculations based on density functional theory (DFT) of the electronic structure and mechanical properties of K2LiAlF6, both non-doped and doped with Cr3+ ions. The densities of states of K2LiAlF6 and the K2LiAlF6:Cr3+ phosphor as well as the crystal-field strength 10Dq, the Cr3+ 2E→4A2 emission energy, elastic constants, bulk and shear moduli, sound velocities and Debye temperature as functions of hydrostatic pressure ranging from 0 up to 40 GPa were calculated. The present DFT calculations indicate that, the band gap of non-doped K2LiAlF6 increases quadratically with increasing pressure. Further, the crystal field strength 10Dq and the 2E→4A2 emission energy, the Debye temperature, sound velocities and shear moduli of Cr-doped K2LiAlF6 increase with increasing pressure, while the 2E→4A2 emission energy becomes red-shifted, which indicates potential applicability of the studied system for pressure sensing. Such calculations for the title system were performed for the first time; the obtained results provide a firm basis for a deeper understanding of physical properties of both neat and doped functional materials

Електронна структура AgCd2GaS4

In the present work we report on measurements of X-ray photoelectron (XP) valence-band spectrum including the comparatively wide energy region corresponding to location of upper core-levels (up to ~80 eV with respect to the bottom of the valence band) of the atoms constituting a quaternary AgCd2GaS4 single crystal grown by the Bridgman method. Electronic structure of AgCd2GaS4 are also theoretically studied by using the first-principles full potential linearized augmented plane wave (FP-LAPW) method. The FP-LAPW method has been employed in the present work to calculate binding energies of upper core-levels for the AgCd2GaS4 compound. With respect to values of binding energies of the Cd 4p, Ag 4p and Ga 3d core-levels, the theoretical and experimental data for the AgCd2GaS4 compound were found to be in agreement to each other. Curves of dominant partial densities of states of AgCd2GaS4 have been compared on a common energy scale with the XP valence-band spectrum of the compound under consideration. ; Рентгенівський фотоелектронний (РФ) спектр валентних електронів монокристалу AgCd2GaS4, вирощеного методом Бріджмена, досліджено в широкому енергетичному інтервалі, котрий уключав спектри внутрішніх електронів, розміщені на відстані аж до ~80 еВ від нижнього краю валентної зони. Електронна структура сполуки AgCd2GaS4 також розрахована «з перших принципів» методом приєднаних плоских хвиль – повного потенціалу (ППХ-ПП). Величини енергій зв’язку (Езв) внутрішніх Cd4p-, Ag4p- i Ga3d-електронів, що отримані теоретично для AgCd2GaS4 за допомогою ППХ-ПП методу, добре збігаються з експериментальними значеннями Езв, котрі виміряні для досліджуваного кристала за допомогою РФ-спектроскопії. Виконано суміщення кривих парціальних щільностей станів складових атомів сполуки AgCd2GaS4 у єдиній енергетичній шкалі з РФ-спектром валентних електронів

Electronic structure of β-RbNd(MoO4)2 by XPS and XES

β-RbNd(MoO4)2 microplates have been prepared by the multistage solid state synthesis method. The phase composition and micromorphology of the final product have been evaluated by XRD and SEM methods. The electronic structure of β-RbNd(MoO4)2 molybdate has been studied employing the X-ray photoelectron spectroscopy (XPS) and X-ray emission spectroscopy (XES). For the molybdate, the XPS core-level and valence-band spectra, as well as XES bands representing energy distribution of the Mo 4d- and O 2p-like states, have been measured. It has been established that the O 2p-like states contribute mainly to the upper portion of the valence band with also significant contributions throughout the whole valence-band region. The Mo 4d-like states contribute mainly to a lower valence band portion

Electronic structure of β-RbNd(MoO4)2 by XPS and XES

β-RbNd(MoO4)2 microplates have been prepared by the multistage solid state synthesis method. The phase composition and micromorphology of the final product have been evaluated by XRD and SEM methods. The electronic structure of β-RbNd(MoO4)2 molybdate has been studied employing the X-ray photoelectron spectroscopy (XPS) and X-ray emission spectroscopy (XES). For the molybdate, the XPS core-level and valence-band spectra, as well as XES bands representing energy distribution of the Mo 4d- and O 2p-like states, have been measured. It has been established that the O 2p-like states contribute mainly to the upper portion of the valence band with also significant contributions throughout the whole valence-band region. The Mo 4d-like states contribute mainly to a lower valence band portion

Searching for better X-ray and gamma-ray photodetectors: structure-composition properties of the TlPb2Br5-xIx quaternary system

Developing X-ray and gamma-ray detectors with stable operation at ambient temperature and high energy resolution is an open challenge. Here, we present an approach to search for new detector materials, combining binary photodetector compounds. More specifically, we explore quaternary TlPb2Br5-xIx compositions, relying on materials synergy between TlBr, TlI, and PbI2 photodetectors. We discover a broad solid solution in the TlPb2Br5-'TlPb2I5' section, which can be derived from a new quaternary compound, TlPb2BrI4, by partial substitution of Br by I atoms on the 4c site or by replacement of I by Br atoms on the 16l site. We carry out a thorough crystallographic analysis of the new TlPb2BrI4 compound and prepare a high-quality standardized structure file. We also complete the phase diagram of the TlPb2Br5-'TlPb2I5' section, based on 21 alloys. Furthermore, we synthesize a series of high quality centimeter-sized TlPb2Br5-xIx single crystals (x = 2, 2.5, 3, 3.5, 4, 4.5) by the Bridgman-Stockbarger method and study their structure and properties using a combination of experimental techniques (X-ray diffraction, X-ray photoelectron spectroscopy, and absorption spectroscopy) and theoretical calculations.ISSN:2633-540

Description of the capacity degradation mechanism in LaNi5-based alloy electrodes

The mechanism of the capacity degradation of LaNi5-based alloy electrodes was investigated with a special focus on the influence of the alloy and surface composition, as well as the unique structure obtained by gas atomisation. The electrochemical properties, especially the cycle life curve (i.e. the capacity as a function of the cycle number of LaNi4.5Al0.5, LaNi2.5Co2.4Al0.1, (La + Mm) Ni3.5Co0.7Al0.35Mn0.4Zr0.05, and MmNi(4.3)Al(0.2)Mn(0.5) alloy electrodes), was analysed and modelled. The capacity degradation upon cycling is determined by the chemical state of the alloy elements and the solubility of their oxides. The cycle life curves for the alloy electrodes without Co exhibited a rapid activation (3-4 cycles to reach maximum capacity), as well as rapid degradation (130-180 cycles for 50% maximum discharge capacity). LaNi2.5Co2.4Al0.1 and (La + Mm) Ni3.5Co0.7Al0.35Mn0.4Zr0.05 alloy electrodes activated after 7-10 cycles and showed very stable discharge behaviour (more than 400 cycles). The Co-containing alloy electrodes primarily lose the cycle stability because of mechanical decrepitation, whereas the alloys without Co suffer from selective dissolution of the unstable elements in the potential window, which was shown by our model of alloy degradation and confirmed by means of SEM, WDX, and ICP-OES data. (C) 2014 Elsevier B.V. All rights reserved