Defect Spinel Structure Research Articles

Decomposition and migration behavior of Pt salt on Al2O3 and SiO2 upon calcination studied by XAFS and UV–visible spectroscopy using a laboratory-type spectrometer

Thermal decomposition behavior of two kinds of Pt salts, namely, H2PtCl6 and Pt(NH3)4Cl2, on amorphous SiO2 and γ-Al2O3 under air to prepare supported platinum catalysts up to 773 K was investigated by in-situ laboratory X-ray absorption fine structure (XANES/EXAFS) and UV–Vis spectroscopy. Changing the oxidation state of platinum species and the coordination environment, the migration to vacant sites or aggregation process on the surface were discussed. The supported H2PtCl6 was reduced to Pt2+ species under air flow around 573 K by eliminating Cl/O ligand atoms until 573 K. High-temperature treatment caused the re-oxidation of the supported Pt species on Al2O3, but it did not affect the oxidation state of SiO2-supported species. The formed platinum oxychloride on Al2O3 was stable under air, but it partly decomposed to atomic-like species above 673 K, followed by migration on the surface, trapping at the cation vacant site because of its defect spinel structure. The lattice oxygen atoms of Al2O3 adjacent to Pt atom captured might cause the re-oxidation, and molecular oxygen was not the oxidant. The partly formed atomic-like species migrates on the SiO2 surface, followed by aggregation to form metallic Pt particles above 573 K.

An investigation into the impact of CuAl2O4 hydrophobization on catalyst structure and performance for syngas conversion

The intricate structure and surface properties of metal oxide catalysts pose a challenge for implementing hydrophobic surface treatment. Herein, the surface of CuAl2O4 catalysts is modified by means of grafting and bridging different saturated fatty acid molecules, including lauric acid, palmitic acid and stearic acid. Consequently, the modification leads to an enhancement in the hydrophobicity of the catalyst, as evidenced by an increase in the static water contact angle from 15.26° to 150.74°. The hydrophobization of CuAl2O4 catalysts, in turn, influences the decomposition and reduction capacity of CuAl2O4, thus favoring the formation of a more stable defective spinel structure and improving the dispersion of Cu particles, thereby restraining aggregation. Notably, the activity results indicate that the hydrophobically modified CuAl2O4 exhibits higher CO conversion and selectivity of dimethyl ether, while effectively suppressing the water–gas shift reaction and reducing CO2 selectivity. This observation points to the significance of the catalyst surface hydrophobicity in enhancing catalytic performance.

Determination of the vacancy distribution over Al cation sites in γ-Al2O3

Correlated experimental and simulated electron diffraction and energy-loss spectroscopy were employed to determine the distribution of Al vacancies in the defective spinel structure of γ-Al2O3, which is important for accurate materials modeling.

Synchrotron Capabilities in a Laboratory Setting: In Situ X-Ray Absorption Spectroscopy of Disordered Vanadium Ferrite Electrodes for Lithium-Ion Batteries

X-ray absorption spectroscopy (XAS) provides important information on metal oxidation state andelement-specific coordination, but data collection has historically required the energy specificityand brilliance of a synchrotron facility. Recent developments in detectors and optics are nowbringing XAS capabilities to the laboratory setting through multiple commercially availableinstruments. At the U.S. Naval Research Laboratory, we use laboratory-based XAS to explore thelocal electronic and atomic structure of a class of disordered vanadium ferrite (VFe2Ox) aerogelsthat exhibit promising performance for electrochemical energy-storage applications such asrechargeable lithium-ion batteries.1,2 These materials are synthesized by an epoxide-promoted sol–gel reaction of iron chloride and vanadium isopropoxide, with the resulting fluid-filled gelsrendered as high surface area aerogels via supercritical-CO2 drying. During the initial sol–gelsynthesis, electroinactive metals such as aluminum, zinc, and zirconium may also be substitutedfor vanadium and iron to alter the local electronic environment and corresponding electrochemicalperformance of VFe2Ox. Heat treatment of as-dried VFe2Ox aerogels under either O2-containingor inert atmosphere yields disordered or nanocrystalline variants, respectively. The resulting seriesof native and substituted VFe2Ox materials are evaluated as powder-composite cathodes versuslithium metal in coin cells with conventional nonaqueous lithium-ion electrolyte. We correlatesuch critical battery-performance parameters as total specific capacity, high-rate capability, andcycle life as a function of VFe2Ox composition and its degree of structural order/disorder, asmeasured with in-situ XANES and EXAFS. In parallel with experimental observations,calculations on VFe2Ox reveal that V incorporates into the defective spinel structure at tetrahedralsites and that both disorder induced by vacancies and Fe/V tetrahedral occupation lowers theoverall energy and opens an electronic energy gap that establishes the redox sequence duringlithiation.1. C. N. Chervin, J. S. Ko, B. W. Miller, L. Dudek, A. N. Mansour, M. D. Donakowski, T.Brintlinger, P. Gogotsi, S. Chattopadhyay, T. Shibata, J. F. Parker, B. P. Hahn, D. R. Rolison,and J. W. Long, J. Mater. Chem. A 3, 12059 (2015).2. C. N. Chervin, R. H. DeBlock, J. F. Parker, B. M. Hudak, N. L. Skeele, J. S. Ko, D. R. Rolison,and J. W. Long, RSC Adv. 11, 14495 (2021).

The Effect of Metal Ratio and Precipitation Agent on Highly Active Iron-Manganese Mixed Metal Oxide Catalysts for Propane Total Oxidation

Iron-manganese mixed metal oxide catalysts with a range of Fe:Mn ratios were synthesised by co-precipitation using sodium carbonate and evaluated for total propane oxidation. The Fe0.50Mn0.50Ox catalyst was the most active, and this was due to increased surface area along with the formation of a Mn2O3 phase that was not present in the other catalysts. The effect of the precipitating agent was evaluated with the Fe0.50Mn0.50Ox catalyst, investigating preparation using (NH4)2CO3, K2CO3, NH4OH, KOH, and NaOH. In almost all cases, the activity of propane oxidation was increased compared to the Na2CO3-prepared catalyst, with the hydroxide-precipitated catalysts generally being more active than the carbonates. The NH4OH catalyst was the best performing and this was thought to be due to the formation of a highly active mixed defect spinel structure. Results demonstrate that highly active mixed metal oxide total oxidation catalysts can be prepared using abundant elements, and the choice of precipitating agent is important to maximise the activity.

Interfacial charge regulation of β-In2S3 photoanode via Tm3+ doping toward enhanced photoelectrochemical performance

The photoelectrochemical properties of the β-In2S3 are seriously restricted by the severe electron-hole pairs recombination. Introducing foreign ions is a powerful means to regulate the properties of β-In2S3, because of its special defect spinel structure. There are few reports that rare earth ion doped β-In2S3 nanosheets improve their photoelectrochemical properties. Herein, a novel nanostructure photoanode was fabricated using Tm3+ doped β-In2S3 by one-pot in situ hydrothermal method. The photoelectrochemical performance has the highest enhancement when the mole ratio of Tm3+ is 1%. The experimental results indicate that the carrier separation and injection efficiency of β-In2S3 after Tm3+ doping are increased to 8.34% and 76.11%, respectively. The introduction of Tm3+ in the β-In2S3 may yield plenty of shallow electron capture levels below conduction band minimum, which can capture photogenerated electrons to promote the separation of electron-hole pair and improve the photoelectrochemical properties of In2S3. This work sheds light on the rare earth ions doped semiconductor photoanode for photoelectrochemical application.

Sonochemical synthesis of supersaturated Ga–Al liquid-alloy fine particles and Al3+-doped γ-Ga2O3 nanoparticles by direct oxidation at near room temperature

In this study, we investigated the fabrication of supersaturated gallium (Ga)–aluminum (Al) liquid alloy and Al3+-doped γ-Ga2O3 nanoparticles (NPs) at near room temperature (60 °C) using sonochemical and sonophysical effects. Supersaturated Ga–Al liquid alloy microparticles (Dav = 1.72 µm) were formed and stabilized at 60 °C by the thermal nonequilibrium field provided by sonochemical hot spots. Compared with liquid Ga, supersaturated Ga–Al liquid alloy was rapidly oxidized to a uniform oxide without Al2O3 or Al deposition. Thus, ultrafine Al3+-doped γ-Ga2O3 NPs were obtained after only 1 h of ultrasonic irradiation at 60 °C. The oxidation of liquid Ga was remarkably accelerated by alloying with metallic Al and ultrasonic irradiation, and the time was shortened. The average diameter and surface area of the γ-Ga2O3-based NPs were 59 nm and 181 m2/g, respectively. Compared with γ-Ga2O3, the optical bandgap of the Al3+-doped γ-Ga2O3 NPs was broadened, and the thermal stability improved, indicating Al3+-doping into the γ-Ga2O3 lattice. However, the lattice constant of γ-Ga2O3 was almost unchanged with or without Al3+-doping. Al3+ was introduced into the defect sites of Ga3+, which were massively induced in the defective spinel structure during ultrasonic processing. Therefore, sonochemical processing, which provides nonequilibrium reaction fields, is suitable for the synthesis of supersaturated and metastable materials in metals and ceramics fields.

Initial nucleation of metastable γ-Ga2O3 during sub-millisecond thermal anneals of amorphous Ga2O3

Beta-phase gallium oxide (β-Ga2O3) is a promising semiconductor for high frequency, high temperature, and high voltage applications. In addition to the β-phase, numerous other polymorphs exist and understanding the competition between phases is critical to control practical devices. The phase formation sequence of Ga2O3, starting from amorphous thin films, was determined using lateral-gradient laser spike annealing at peak temperatures of 500–1400 °C on 400 μs to 10 ms timescales, with transformations characterized by optical microscopy, x-ray diffraction, and transmission electron microscopy (TEM). The resulting phase processing map showed the γ-phase, a defect-spinel structure, first nucleating under all annealing times for temperatures from 650 to 800 °C. The cross-sectional TEM at the onset of the γ-phase formation showed nucleation near the film center with no evidence of heterogeneous nucleation at the interfaces. For temperatures above 850 °C, the thermodynamically stable β-phase was observed. For anneals of 1–4 ms and temperatures below 1200 °C, small randomly oriented grains were observed. Large grains were observed for anneals below 1 ms and above 1200 °C, with anneals above 4 ms and 1200 °C resulting in textured films. The formation of the γ-phase prior to β-phase, coupled with the observed grain structure, suggests that the γ-phase is kinetically preferred during thermal annealing of amorphous films, with β-phase subsequently forming by nucleation at higher temperatures. The low surface energy of the γ-phase implied by these results suggests an explanation for the widely observed γ-phase inclusions in β-phase Ga2O3 films grown by a variety of synthesis methods.

Improvement of high-temperature energy storage performance in polymer dielectrics by nanofillers with defect spinel structure

The electrostatic energy storage performance of polymer dielectrics at high temperature and high electric field can be significantly improved by the incorporation of wide-bandgap, nano-sized particles. It is traditionally believed that the embedded nanoparticles can scatter the hot charges and lead to charge trapping in the interfacial region, which suppress the conduction loss and promote the energy storage performance. In this work, the nano-sized γ-Al2O3 with cubic defect spinel structure and nano-sized α-Al2O3 with a wider bandgap are introduced into a heat-resistant dielectric polymer, respectively, to form two different nanocomposites. The field-dependent energy storage performance, electrical conductivity, and breakdown strength of the polymer nanocomposites at high temperatures, as well as the thermally stimulated depolarization current, are investigated. The results indicate that the intrinsic deep traps introduced by γ-Al2O3 with cubic defect spinel structure are a more critical factor in improving the energy storage performance of the polymer-based composites. We anticipate that our findings reported in this work may help to better guide the selection of nanofillers for high-temperature dielectric polymer nanocomposites.

Thermal stability of MnO2 polymorphs

This study reports thermal stability of α, β, γ, δ, and λ-type MnO2 polymorphs investigated using differential scanning calorimetry (DSC) and in-situ high-temperature X-ray diffraction measurement (HTXRD). These experiments revealed that the thermal stability of the polymorphs is in the following order: β ​> ​α ​> ​γ ​> ​δ ​≈ ​λ. The β-MnO2 phase (1 ​× ​1 tunnel, rutile structure), the most stable form between the MnO2 polymorphs, maintains the structure up to 500 ​°C until oxygen release causes phase transformation to Mn2O3. The α-MnO2 phase (2 ​× ​2 and 1 ​× ​1 tunnel structure) exhibits high thermal stability comparable to the β phase, despite its large vacant 2 ​× ​2 tunnel. The γ-MnO2 phase (mixed microdomain structure of 2 ​× ​1 tunnel and 1 ​× ​1 tunnel) shows a stepwise transformation into β-MnO2 from 400 ​°C after structure relaxation. The δ-MnO2 phase (layered structure) is easily destabilized by extracting interlayer K ions, resultingly, to lose the interlayer periodicity below 200 ​°C, while each layer itself is preserved up to ∼500 ​°C. The λ-MnO2 phase (defect spinel structure) is thermally unstable and transforms into β-MnO2 around 250 ​°C, and subsequently decomposes to Mn2O3 above the temperature. The thermal stability of MnO2 polymorphs is discussed in terms of the bonding environment of oxide ions.

Reversible Cation‐Mediated Anionic Redox in Defect Spinel Structure for High Power Batteries

AbstractWith ever‐increasing energy demand, more efforts are dedicated to designing innovative electrode materials providing higher storage capability and power output. As it has been demonstrated recently, the use of mixed cation–anion redox reactions opens up new possibilities for the significant rise of material's capacity and unusual electrochemical characteristics of lithium‐ion battery electrodes. In this paper, a new type of fast cation‐mediated anionic redox reaction in the 3D spinel structure is presented. Li0.98K0.01Mn1.86Ni0.11O4 shows 170% of stoichiometric spinel theoretical capacity without voltage hysteresis or significant capacity and voltage fading attributed to limitations of reversible anionic redox. The authors’ sol–gel‐derived defect spinel structure can deliver 250 mAh g−1 at 1C and retain 64% of this capacity under a high 50C current rate. The observed electrochemical process shows the reversibility unseen before in mixed cation–anion redox cathode materials for Li‐ion systems.

A novel Yb3+/Tm3+ co-doped semiconductor sensitized up-conversion strategy for β-In2S3 photoanode with enhanced photoelectrochemical properties

N-type β-Indium sulfide (β-In2S3) has emerged as one of the most promising semiconductor photoanode for use in photoelectrochemical water-splitting in recent years, its defective spinel structure facilitates the incorporation of foreign ions to adjust the photoelectrochemical (PEC) performance. Lanthanide ions with excellent optical properties and abundant energy level structure have attracted much attention. In this study, the semiconductor sensitized up-conversion strategy was first applied to improve the PEC performance of β-In2S3 by inhibiting electron-hole pairs recombination. Yb3+/Tm3+ co-doped β-In2S3 (YTS) were successfully prepared on FTO substrate in-situ as PEC water splitting photoanode by a simple hydrothermal method, the effects of Yb3+/Tm3+ co-doping on PEC properties, charge-transport properties and energy band structure are discussed. When Yb3+ ions in the total cations of precursor accounted for 3%, and Tm3+ ions accounted for 0.5%, the photocurrent density of Yb3+/Tm3+ co-doped β-In2S3 (YTS-3) is 0.42 mA/cm2 (0.5 V vs. Ag/AgCl), which is about 1.68 times higher than pure β-In2S3 (0.25 mA/cm2). No photocurrent response was detected under 980 nm single-wavelength LED, proving that host material sensitization is more effective than direct excitation. The improved PEC properties for Yb3+/Tm3+ co-doped β-In2S3 might be attributed to the semiconductor sensitized up-conversion strategy, which realize a cycle of energy released by electron-hole pairs recombination. Moreover, the donor states formed after doping inhibits the recombination of electron-hole pairs by capturing electrons. The ways that the Yb3+/Tm3+ dopants modified the energy band structure and PEC properties of β-In2S3 demonstrated in this study have guiding significance for the design of lanthanide ions doped semiconductor photoanode.

Epitaxial growth of γ-(AlxGa1-x)2O3 alloy thin films on spinel substrates via mist chemical vapor deposition

Among the five polymorphs of α, β, γ, δ, and κ(ε)-gallium oxide (Ga2O3), we focused on metastable cubic γ-Ga2O3, which exhibits a defect spinel structure, from the viewpoint of lattice matching. Alloying γ-Ga2O3 with γ-aluminum oxide (γ-Al2O3), which exhibits the same crystal structure as that of the former, is effective for lattice-matched growth on a spinel substrate as well as band gap engineering. At the composition ratio x = 0.48, γ-aluminum gallium oxide (γ-(AlxGa1-x)2O3) lattice matched to the spinel substrate, and its band gap energy increased to 5.88 eV. Thus, γ-(AlxGa1-x)2O3 is a promising material for wide band gap semiconductors that are lattice matched to the substrates, for applications in power-switching devices and deep-ultraviolet optoelectronics. In this study, we demonstrated the epitaxial growth of γ-(AlxGa1-x)2O3 alloy thin films on spinel substrates using mist chemical vapor deposition. At the Al concentration of 0.11 M, the epitaxial γ-(AlxGa1-x)2O3 thin film was successfully grown with Laue-oscillations observed in the X-ray diffraction 2θ–ω scan. Moreover, transmission electron microscopy measurements revealed that the γ-(AlxGa1-x)2O3 thin film was lattice matched and grown on the spinel substrate with few misfit dislocations at the interface. Band gap engineering was achieved in the range of 5.0–6.0 eV by estimating the direct band gap energy. Thus, our results, which indicate the possibility of limited dislocations due to lattice matches, are expected to facilitate the development of materials with wider band gaps based on γ-(AlxGa1-x)2O3.

Ni catalysts for dry methane reforming prepared by A-site exsolution on mesoporous defect spinel magnesium aluminate

In dry methane reforming, the selection of a suitable support is critical due to coke formation and metal particle sintering. We prepared two types of mesoporous defect spinel magnesium aluminate support, namely DS09, with a Mg/Al molar ratio (Mg/Al) of 0.1, and DS19 with Mg/Al = 0.24. Each support has a high surface area, large mesopore volume, and a phase between its defect spinel (Mg0.388Al2.408O4) and spinel (MgAl2O4) structures. Magnesium aluminate with a Mg/Al of 0.5 (MG30), which has a low surface area and is devoid of mesopores, was used as the reference support. Ni was supported on DS09 (Ni-DS09) and DS19 (Ni-DS19) by A-site exsolution. These catalysts display significant advantages over Ni-supported MG30 (Ni-MG30); Ni-DS19 exhibited a higher coke resistance than Ni-DS09, due to its lower acidity, while DS19, which contains a defect spinel structure, optimized acidity, and well-developed mesopores, was the best support for the DMR.

Remaining Li-Content Dependent Structural Evolution during High Temperature Re-Heat Treatment of Quantitatively Delithiated Li-Rich Cathode Materials with Surface Defect-Spinel Phase.

Pre-extracting Li+ from Li-rich layered oxides by chemical method is considered to be a targeted strategy for improving this class of cathode material. Understanding the structural evolution of the delithiated material is very important because this is directly related to the preparation of electrochemical performance enhanced Li-rich material. Herein, we perform a high temperature reheat treatment on the quantitatively delithiated Li-rich materials with different amounts of surface defect-spinel phase and carefully investigate the structural evolution of these delithiated materials. It is found that the high temperature reheat treatment could cause the decomposition of the unstable surface defect-spinel structure, followed by the rearrangement of transition metal ions to form the thermodynamically stable phases, More importantly, we find that this process has high correlation with the remaining Li-content in the delithiated material. When the amount of extracted Li+ is relatively small (corresponding to the higher remaining Li-content), the surface defect-spinel phase could be dominantly decomposed into the LiMO2 (M = Ni, Co, and Mn) layered phase along with the significant improvement of electrochemical performance, and continuing to decrease remaining Li-content could lead to the emergence of M3O4-type spinel impurity embedding in the final product. However, when the extracted Li+ further achieves a certain amount, after the high temperature heat-treatment the Mn-rich Li2MnO3 phase (C2/m) could be separated from Ni-rich phases (including R3m, Fd3m, and Fm3m), thus resulting in a sharp deterioration of initial capacity and voltage. These findings suggest that reheating the delithiated Li-rich material to high temperature may be a simple and effective way to improve the predelithiation modification method, but first the amount of extracted Li+ should be carefully optimized during the delithiation process.

In situ TEM study of κ→β and κ→γ phase transformations in Ga2O3

The temperature-driven phase transformation of metastable κ-Ga2O3 layers deposited on sapphire was studied by high resolution TEM. Annealing experiments up to 1000 °C were performed either in situ in vacuum within the TEM or ex situ in ambient air. This allowed for the detection of the atomistic mechanisms at the basis of κ to β phase transition. In the case of in situ TEM observations we could even record in real time the atomic rearrangement. We provide in this paper the relevant crystallographic relations between original κ and new β lattice.Surprisingly, the ex situ experiments demonstrated the additional formation of a γ-Ga2O3 intermediate phase at 820 °C. The remarkably different behavior between in situ and ex situ annealing experiments is explained in terms of ambient (ambient air or high vacuum) and heating rate.An extensive investigation of γ-Ga2O3, also a metastable phase, showed that it has a cubic defect spinel structure (Fd3¯m) with disordered vacancies. Repeated observations of the metastable γ-Ga2O3 after two months show that the vacancies tend to order, and that the vacancies are fully ordered after one year.

Phase composition and transformations in magnetron-sputtered (Al,V)2O3 coatings

Coatings of (Al1-xVx)2O3, with x ranging from 0 to 1, were deposited by pulsed DC reactive sputter deposition on Si(100) at a temperature of 550 °C. XRD showed three different crystal structures depending on V-metal fraction in the coating: α-V2O3 rhombohedral structure for 100 at.% V, a defect spinel structure for the intermediate region, 63–42 at.% V. At lower V-content, 18 and 7 at.%, a gamma-alumina-like solid solution was observed, shifted to larger d-spacing compared to pure γ-Al2O3. The microstructure changes from large columnar faceted grains for α-V2O3 to smaller equiaxed grains when lowering the vanadium content towards pure γ-Al2O3. Annealing in air resulted in formation of V2O5 crystals on the surface of the coating after annealing to 500 °C for 42 at.% V and 700 °C for 18 at.% V metal fraction respectively. The highest thermal stability was shown for pure γ-Al2O3-coating, which transformed to α-Al2O3 after annealing to 1100 °C. Highest hardness was observed for the Al-rich oxides, ~24 GPa. The latter decreased with increasing V-content, larger than 7 at.% V metal fraction. The measured hardness after annealing in air decreased in conjunction with the onset of further oxidation of the coatings.

Heteroepitaxial growth of α-, β-, γ- and κ-Ga2O3 phases by metalorganic vapor phase epitaxy

Improved MOVPE (metalorganic vapor phase epitaxy) growth conditions for the different Ga2O3 phases are reported. The influence of the substrate material, the growth conditions and the variation of precursors on the phase formation was investigated. Trimethylgallium (TMG) and N2O were used as common precursors for gallium and oxygen, respectively. In addition, water was supplied for the growth of κ-Ga2O3. The influence of additional triethylboron (TEB) and dimethylhydrazin (DMHy) on the formation of the α-phase is discussed. Growth conditions could be determined, where α-, β-, γ- and κ-Ga2O3 is epitaxially deposited. The κ-phase was epitaxially grown on c-, a- and r-plane Al2O3, (1 1 1) MgO, (1 1 1) MgAl2O4 and on a (0 0 0 1) Al2O3/(0 0 0 1) GaN heterostructure. Successful MOVPE growth of γ-Ga2O3 with defect spinel structure has been achieved on (0 0 0 1) Al2O3, (1 1 1) and (1 0 0) MgAl2O4, (1 0 0) MgO as well as on (0 0 0 1) Al2O3/(0 0 0 1) GaN. Boron addition stabilizes the MOVPE growth of the α-phase on c-, a- and r-plane Al2O3. The various Ga2O3 phases were identified by X-ray diffraction (XRD). The epitaxial relationships between the Ga2O3 phases and the different substrates were determined.Optical transmission spectra measured in the spectral range from 200 to 2000 nm show a well-defined absorption edge at about 4.9 eV for layers of β-, γ- and κ-Ga2O3 and 5.3 eV for layers of α-Ga2O3 grown on c-plane sapphire.

Carmeltazite, ZrAl2Ti4O11, a New Mineral Trapped in Corundum from Volcanic Rocks of Mt Carmel, Northern Israel

The new mineral species carmeltazite, ideally ZrAl2Ti4O11, was discovered in pockets of trapped melt interstitial to, or included in, corundum xenocrysts from the Cretaceous Mt Carmel volcanics of northern Israel, associated with corundum, tistarite, anorthite, osbornite, an unnamed REE (Rare Earth Element) phase, in a Ca-Mg-Al-Si-O glass. In reflected light, carmeltazite is weakly to moderately bireflectant and weakly pleochroic from dark brown to dark green. Internal reflections are absent. Under crossed polars, the mineral is anisotropic, without characteristic rotation tints. Reflectance values for the four COM wavelengths (Rmin, Rmax (%) (λ in nm)) are: 21.8, 22.9 (471.1); 21.0, 21.6 (548.3), 19.9, 20.7 (586.6); and 18.5, 19.8 (652.3). Electron microprobe analysis (average of eight spot analyses) gave, on the basis of 11 oxygen atoms per formula unit and assuming all Ti and Sc as trivalent, the chemical formula (Ti3+3.60Al1.89Zr1.04Mg0.24Si0.13Sc0.06Ca0.05Y0.02Hf0.01)Σ=7.04O11. The simplified formula is ZrAl2Ti4O11, which requires ZrO2 24.03, Al2O3 19.88, and Ti2O3 56.09, totaling 100.00 wt %. The main diffraction lines, corresponding to multiple hkl indices, are (d in Å (relative visual intensity)): 5.04 (65), 4.09 (60), 2.961 (100), 2.885 (40), and 2.047 (60). The crystal structure study revealed carmeltazite to be orthorhombic, space group Pnma, with unit-cell parameters a = 14.0951 (9), b = 5.8123 (4), c = 10.0848 (7) Å, V = 826.2 (1) Å3, and Z = 4. The crystal structure was refined to a final R1 = 0.0216 for 1165 observed reflections with Fo > 4σ(Fo). Carmeltazite exhibits a structural arrangement similar to that observed in a defective spinel structure. The name carmeltazite derives from Mt Carmel (“CARMEL”) and from the dominant metals present in the mineral, i.e., Titanium, Aluminum and Zirconium (“TAZ”). The mineral and its name have been approved by the IMA Commission on New Minerals, Nomenclature and Classification (2018-103).

Stabilizing the metastable γ phase in Ga2O3 thin films by Cu doping

The metastable cubic γ phase Ga2O3 with a defect spinel structure presents several fascinating properties, which may be a more attractive material than the stable β form. Herein, we found that the metastable γ-Ga2O3 can be stabilized by copper (Cu) doping through a simple operation and low cost method of sol-gel. The γ-Ga2O3 thin films were prepared under the annealing of 700 °C in nitrogen atmosphere for Cu doping. The β phase Ga2O3 ones were obtained at the same condition without the Cu dopant. While the Cu doped γ phase Ga2O3 will transform to β phase for a high annealing temperature above 800 °C. The grain size of Cu doped γ-Ga2O3 and undoped β-Ga2O3 thin films increases with the increase of the annealing temperature. The UV–Vis absorption spectrum of the β-Ga2O3 thin film exhibits a sharp intrinsic absorption edge at ∼250 nm, whilst Cu doped γ-Ga2O3 thin film displays an obvious red-shift. The band gap decreases from 4.90 eV to 4.38 eV for the Cu doping. The photoluminescence intensity at the ultraviolet and blue region of Cu doped γ-Ga2O3 thin films are stronger than undoped β-Ga2O3, which can be attributed to the introduction of more defects such as oxygen vacancies in γ phase by Cu doping.