Annealing behaviour of vapour-deposited Ni-Te thin films

Vapour-deposited phases in the Ni-Te system show interesting properties after annealing. Pulse-annealed thin films of NiTe₂ alloy show the presence of an ordered cubic phase with the lattice parameter a = 0.74 nm (temperature approximately 473 K). On further annealing (temperature approximately 513 K) this ordered structure transforms to a long-period phase and finally a highly disordered structure results. All these transformations are of an irreversible nature. The mechanism of these transformations and the nature of the disorder will be discussed.     

Explosive crystallization in the course of formation of Se/Ag nanosize film structure

Results of an experimental study of explosive crystallization appearing in the process of formation of a Se/Ag nanosize film structure are presented. It is shown that explosive crystallization appears in a wide range of Se film thicknesses (70–280 nm) and occurs during a narrow time interval (2.00–4.52 s). The cooperative effect of the thermal energy of the phase transformation of Ag₂Se and the energy of elastic stress in the amorphous Se film leads to development of an explosive crystallization. It was found that, depending on the relative thicknesses of Se and Ag films, orthorhombic Ag₂Se with crystal-lattice constants a = 4.333 Å, b = 7.062 Å, and c = 7.764 Å and hexagonal Se (a = 4.3552 Å and c = 4.9495 Å) are formed in the reaction products upon the explosive crystallization.     

Electrical properties of silver selenide thin films prepared by reactive evaporation

The electrical properties of silver selenide thin films prepared by reactive evaporation have been studied. Samples show a polymorphic phase transition at a temperature of 403 ± 2 K. Hall effect study shows that it has a mobility of 2000 cm²V^?1s^?1 and carrier concentration of 10¹⁸ cm^?3 at room temperature. The carriers are ofn-type. X-ray diffraction study indicates that the as-prepared films are polycrystalline in nature. The lattice parameters were found to bea= 4.353 Å,b= 6.929 Å andc = 7.805 Å.     

Implantation of carbon into thin iron films

Polycrystalline iron films, 1000 Å thick, were implanted with carbon ions at 38 kV to an average concentration of 6 at.%. After implantation and subsequent annealing, lattice parameter and microstructural determinations were made with transmitted electrons. Immediately after implantation, the carbon is retained in supersaturated solid solution and the lattice type is transformed from the normal body-centered cubic of alpha iron to body-centered tetragonal with a c/a ratio of 1.6. After annealing above 330 °C for several hours, the carbon precipitates from solid solution as a carbide phase and the c/a ratio is reduced. These results can be interpreted in terms of the formation and annealing of the metastable martensite constituent of the iron-carbon system.     

The crystal structure of a new sodium zinc arsenate phase solved by “simulated annealing”

The framework structure of a new sodium zinc arsenate, produced by dehydration of the Na₆(ZnAsO₄)₆·8 H₂0 sodalite analog, has been solved by a simulated annealing method. This method utilizes typical tetrahedral-atom bonding schemes with possible space group and unit cell dimensions to randomly generate possible continuous frameworks and their calculated energies. The Rietveld refinement of the Na₆(ZnAsO₄)₆ solution phase was initially performed on room temperature X-ray data and then continued on low-temperature constant wavelength neutron data. This sodium zinc phosphate is a hexagonal polycrystalline material: space group P6₃ (no. 173), with a = b =9.005 (2) Å, c = 8.161 (2) Å, a = β = 90°, γ = 120°, V= 573.1 Å, and Z = 2, with R = 12.35% and R_w = 9.76% for 2756 (CW neutron) powder data points. This tridymite structural analog undergoes a room-temperature transformation to the open-framework sodalite structure.     

A new carbon structure in annealed film coatings of the carbon–lead system

Carbon–lead solid solutions coexisting with amorphous carbon have been obtained for the first time in a film coating deposited by ion-plasma sputtering. During subsequent vacuum annealing of carbon–lead films containing more than 68.5 at % Pb, this element almost completely evaporates to leave an amorphous carbon coating on a substrate. During annealing at 1100°C, this amorphous carbon crystallizes into a new hexagonal lattice with unit cell parameters a = 0.7603 nm and c = 0.8168 nm. Characteristic X-ray diffraction data for the identification of this phase are determined.

     

Influence of post-deposition annealing on the microstructure and properties of Ga2O3:Mn thin films deposited by RF planar magnetron sputtering

Thin films of Ga₂O₃:Mn have been deposited on silicon (100) substrates without intentional heating by radio frequency (RF) planar magnetron sputtering from a Mn-doped Ga₂O₃ target in an oxygen-argon mixture atmosphere. Microstructure and properties of the deposited Ga₂O₃:Mn films were systematically investigated as a function of the post-deposition annealing temperature in the range between 500 °C and 1200 °C. X-ray diffraction (XRD) measurements showed that the as-deposited Ga₂O₃:Mn films were of an amorphous structure in nature. The Ga₂O₃:Mn films became crystalline by the post-deposition annealing above 800 °C and the crystallinity of the films was continuously improved up to the annealing temperature of 1200 °C. It was shown that the annealed Ga₂O₃:Mn films possessed a monoclinic β-Ga₂O₃ phase having a textured structure with (400) and (?401) crystallographic planes oriented preferentially parallel to the substrate surface. The lattice parameters of the monoclinic β-Ga₂O₃ phase in the 1200 °C annealed Ga₂O₃:Mn films were measured to be a = 12.152 Å, b = 3.043 Å, and c = 5.785 Å.     

Thermal oxidation of β-Ta below 500 °C

Results are presented for the thermal oxidation behaviour of two types of β-Ta thin films below 500 °C. The thin films investigated were composed of the pure phase with no other observable phases or of mixtures containing b.c.c. tantalum and TaO_z phases. Their crystalline structures were investigated by X-ray diffraction, and their compositions were determined by Auger electron spectroscopy combined with in situ ion sputtering.We showed that the allowable cell expansion of β-Ta due to the incorporation of interstitial oxygen at elevated temperature is less than 3.5% irrespective of the contents of the mixed phases. The oxidation proceeds via the precipitation of the suboxide related to the cubic oxide with cell constants a of 3.95 Å and 7.90 Å respectively with the subsequent formation of amorphous Ta₂O₅. The effects of annealing of the heat-treated thin films show that the suboxide has a very stable structure. The TaO_z phase is not observed during the “normal” oxidation process in air of β-Ta films with thicknesses between 1000 and 4000 Å, but it is observed when thin films incorporating certain amounts of oxygen are treated above 500 °C with no supply of oxygen from the atmosphere.     

Crystal structures of Ln<Subscript>2</Subscript>TiO<Subscript>5</Subscript> (Ln = Gd,Dy) polymorphs

Single crystals of four Ln₂TiO₅ polymorphs have been grown, and their structures have been determined: orthorhombic (Gd₂TiO₅, a = 10.460(5), b = 11.317(6), c = 3.750(3) Å, Pnam, Z = 4), hexagonal (Gd_1.8Lu_0.2TiO₅, a = 3.663(3), c = 11.98(1) Å, P6₃/mmc, Z = 1.2), cubic (Dy₂TiO₅, a = 10.28(1) Å, Fd3m, Z = 10.4), and monoclinic (Dy₂TiO₅, a = 10.33(1), b = 3.653(5), c = 7.306(6) Å, β = 90.00(7)°, B2/m, Z = 2.4). The last polymorph has been identified for the first time.     

Spontaneous explosive crystallization and phase formation in a nanosized selenide/indium heterostructure

Spontaneous explosive crystallization in a nanosized Se/In heterostructure is experimentally studied. It is demonstrated that spontaneous explosive crystallization in this structure occurs in a wide (70–280 nm) Se thickness range in the narrow time interval of 1.7–3.5 s. It is established that, depending on the Se and In thickness ratio, in reaction product spontaneous explosive crystallization results in the formation of hexagonal InSe with the crystal lattice parameters a = 4.05 Å and c = 16.93 Å and hexagonal Se with a = 4.3662 Å and c = 4.9536 Å.     

Enhanced photocatalytic activity of Mg0.05Zn0.95O thin films prepared by sol–gel method through a cycle

Mg_0.05Zn_0.95O thin films were prepared on silicon substrates by a sol–gel dip-coating technique. Microstructure, surface topography and optical properties of the thin films were characterized by X-ray diffraction, atom force microscopy, Fourier transform infrared spectrophotometer and fluorescence spectrometer. The results show that the thin film annealed at 700 °C has the largest average grain size and exhibits the best c-axis preferred orientation. As annealing temperature increases to 800 °C, the grain along c-axis has been suppressed. Roughness factor and average particle size increase with the increase of annealing temperature. The IR absorption peak appearing at about 416 cm^?1 is assigned to hexagonal wurtzite ZnO. The thin film annealed at 700 °C has the maximum oxygen vacancy, which can be inferred from the green emission intensity. Photocatalytic results show that the thin film annealed at 700 °C exhibits remarkable photocatalytic activity, which may be attributed to the larger grain size, roughness factor and concentration of oxygen vacancy. Enhanced photocatalytic activity of Mg_0.05Zn_0.95O thin films after a cycle may be attributed to the increase of surface oxygen vacancy and photocorrosion of amorphous MgO on the surface of thin film under UV irradiation.     

Metastable structures of liquid-quenched and vapour-quenched antimony films

Antimony foils/films have been prepared by liquid-quenching and by vapour-quenching. (1) Simple cubic (a=3.16 Å), (2) f c c (a=4.61 Å), (3) tetragonal (a=3.01 Å, c=4.96 Å and c/a=1.64) structures, and (4) a new rhombohedral (a _H=4.12 Å, c _H=10.26 Å and c _H/a _H=2.49) metastable structure have been observed in splat-quenched foils. The metastable rhombohedral phase transforms to the equilibrium rhombohedral phase (a _H=4.30 Å, c _H=11.27 Å and c _H/a _H=2.62) on heating. The simple cubic, f c c and tetragonal phases are converted in to a hexagonal close-packed (a=3.33 Å, c=5.23 Å and c/a=1.57) structure on heating in the electron microscope. The simple cubic and h c p phases correspond to the known high-pressure phases of antimony. The h c p phase does not transform on further heating. Films prepared by vapour deposition on substrates held at room temperature show the same metastable f c c and rhombohedral phases as observed in splat-quenched foils, in addition to the equilibrium rhombohedral phase. On heating, these metastable phases transform in the same way as the splat-quenched specimens. The films deposited at liquid air temperature are amorphous; on electron-beam heating, these crystallize first to an unidentified complicated structure and then to the equilibrium structure.     

Electron diffraction study of the ordering process in Cu2−xS

The formation of the ordered phase of Cu_2?xS (x=0.2) and its structural transformations were investigated. It is shown that the ordered Cu_2?xS phase is formed from face-centred cubic (f.c.c.)Cu_2?xS as a result of a phase transition which is caused by copper enrichment during heat treatment at temperatures in the range 100–300°C. The ordered phase exists in the temperature range from room temperature to 300°C. This phase transforms reversibly to the f.c.c. phase at about 300°C. Compositional changes occur on further heat treatment of the ordered phase and lead to the irreversible transformation of Cu_2?xS to the hexagonal modification of Cu₂S.     

Thermal Conductivity of Tetragonal Cadmium Diphosphide Crystals

Tetragonal cadmium diphosphide (β-CdP₂) single crystals with high structural perfection have been grown and their thermal conductivity has been measured. The results indicate that the higher thermal conductivity across the c axis corresponds to the smaller unit-cell parameter of the crystals (a = 5.08 ± 0.01 Å and c = 18.59 ± 0.05 Å). The observed thermal conductivity anisotropy is tentatively attributed to the fact that structural basis of β-CdP₂ is made up of spectral phosphorus chains running in the [100] and [010] directions.     

High-pressure,high-temperature study of GeS2 and GeSe2

Phase transitions of the GeX₂ (X = S, Se) dichalcogenides have been studied at pressures of up to p ? 8 GPa and temperatures from 675 to 1375 K, and portions of their p-T phase diagrams have been constructed using our and previous experimental data. The crystal structure of the GeS₂-III phase has been refined by the Rietveld method (HgI₂ structure, P4₂/nmc, a = 3.46906(2) Å, c = 10.9745(1) Å, Z = 2, D _x = 3.438 g/cm³, R = 0.06). GeSe₂-III crystals have been grown for the first time at p ? 7 GPa in the temperature range 875–1275 K. The unit-cell parameters of GeSe₂-III (hex) are a = 6.468 ± 0.004 Å and c = 24.49 ± 0.10 Å (D _meas = 5.16 g/cm³, D _x = 5.18 g/cm³, Z = 12).     

Preparation and crystal structure characterization of CuNiGaSe<Subscript>3</Subscript> and CuNiInSe<Subscript>3</Subscript> quaternary compounds

Samples of the quaternary chalcogenide compounds, CuNiGaSe₃ and CuNiInSe₃, prepared by direct fusion and annealing method, were characterized by X-ray powder diffraction. In each case, the crystal structure was refined using the Rietveld method. Both compounds were found to crystallize in the tetragonal system, space group P \(\bar 4\)2c (N°112), with unit cell parameter values a = 5.6213(1) Å, c = 11.0282(3) Å, V = 348.48(1) ų and a = 5.7857(2) Å, c = 11.6287(5) Å, V = 389.26(3) ų for CuNiGaSe₃ and CuNiInSe₃, respectively. These compounds have a normal adamantane structures and are isostructural with CuFeInSe₃.     

Mutual phase stabilization of aluminium phosphate and titania in AlPO4-TiO2 binary system

Crystallization behaviour of amorphous aluminium phosphate (AlPO₄) and titania (TiO₂) in a mixed system of the two (5:1) has been reviewed in the light of our recent results. The polymorphous aluminium phosphate in such a binary system grows exclusively in a single phase over a temperature range 500–1150°C. The phase is reported to have a tridymite-like structure belonging to orthorhombic system with cell parametersa=9·638±0·0019,b=8·664±0·0017 andc=18·280±0036Å. Titania in the system preferentially retains its anatase phase morphology up to a temperature (950°C) well beyond its normal anatase → rutile transformation temperature showing a phenomenon of stabilization of this phase in such mixture. An interfacial reaction mechanism that can explain the observed phenomenon of mutual phase stabilization has been discussed and implications of this result towards the use of such technique for stabilization of various polymorphous compounds in a single phase has been pointed out.     

Alloying behaviour,thermal stability and phase evolution in quinary AlCoCrFeNi high entropy alloy

An equiatomic quinary AlCoCrFeNi high entropy alloy (HEA) has been synthesized by mechanical alloying. Milled powder after 30?h shows good chemical homogeneity and refined morphology with a mean particle size of ～4?μm. Solid solution phase with BCC crystal structure (a?=?2.89?±?0.02?Å) has been confirmed from XRD and transmission electron microscopy in the as-synthesized high entropy alloy. The milled alloy powder is not thermally stable. Differential scanning calorimetric (DSC) thermogram of 30?h milled powder exhibits the presence of a small peak at ～600?°C (873?K) with a thermal shift near the peak. This thermal shift indicates the diffusive type of phase transformation in this alloy while heating. The analysis of the in-situ heating X-ray diffraction patterns at various temperatures extends support to the diffusive nature of the phase transformation. Upon heat treatment, the disordered BCC solid solution phase partially transforms to Ni₃Al prototype L1₂ phase which precipitates at a lower temperature (350?°C (623?K)) as observed by in-situ XRD experiments. However, at high temperature annealing (575–800?°C (848–1073?K)) the evolution of a partially ordered BCC phase (B2) with lattice parameter (a?=?2.87?±?0.02?Å), and L1₂ phase (a?=?3.58?±?0.05?Å), along with tetragonal σ phase (a?=?8.8?Å and c?=?4.53?Å) are observed. Similar types of phases have also been identified after annealing and microwave sintering at 800?°C (1073?K) & 900?°C (1173?K) respectively. The transformation of ordered BCC phases along with two intermetallics such as L1₂ phase and σ phase suggests that the evolution of the high entropy phase in the milled condition leads to a combination of high entropy and medium entropy phases in the annealed condition.     

Compounds WAl<Subscript>4</Subscript>, WAl<Subscript>3</Subscript>, W<Subscript>3</Subscript>Al<Subscript>7</Subscript>, and WAl<Subscript>2</Subscript> and Al-W-N combustion products

X-ray diffraction data are presented for combustion products in the Al-W-N system. New, nonequilibrium intermetallic compounds have been identified, their diffraction patterns have been indexed, and their unit-cell parameters have been determined. The phases α-and β-WAl₄ are shown to exist in three isomorphous forms, differing in unit-cell centering. The phases α′-, α″-, and α?-WAl₄ are monoclinic, with a ₀ = 5.272 Å, b ₀ = 17.770 Å, c ₀ = 5.218 Å, β = 100.10°; point groups C12/c1, A12/n1, I12/a1, respectively. The phases β′-, β″-, and β?-WAl₄ are monoclinic, with a ₀ = 5.465 Å, b ₀ = 12.814 Å, c ₀ = 5.428 Å, β = 105.92°; point groups A112/m, B112/m, I112/m, respectively. The compounds WAl₂ and W₃Al₇, identified each in two isomorphous forms, differ in cell metrics (doubling) but possess the same point group: P222. WAl ₂ ^′ : orthorhombic, a ₀ = 5.793 Å, b ₀ = 3.740 Å, c ₀ = 6.852 Å. WAl ₂ ^″ : orthorhombic, a ₀ = 11.586 Å, b ₀ = 3.740 Å, c ₀ = 6.852 Å. W₃Al ₇ ^′ : orthorhombic, Pmm2, a ₀ = 6.225 Å, b ₀ = 4.806 Å, c ₀ = 4.437 Å. W₃Al ₇ ^″ : orthorhombic, Pmm2, a ₀ = 12.500 Å, b ₀ = 4.806 Å, c ₀ = 8.874 Å. The new phase WAl₃: triclinic, P1, a ₀ = 8.642 Å, b ₀ = 10.872 Å, c ₀ = 5.478 Å, α = 104.02°, β = 64.90°, γ = 107.15°.     

Phase relations and properties of alloys in the SnSe-DySe system

Phase relations in the SnSe-DySe system have been studied using differential thermal analysis, X-ray diffraction, microstructural analysis, microhardness tests, and density measurements, and its T-x phase diagram has been mapped out. The SnSe-DySe system contains a new ternary compound with the composition DySnSe₂, which crystallizes in orthorhombic symmetry with unit-cell parameters a = 5.74 ± 0.02 Å, b = 10.49 ± 0.03 Å, and c = 11.66 ± 0.05 Å (Z = 7, V = 702 ų, measured density ρ_meas = 7.02 g/cm³, X-ray density ρ_x = 7.26 g/cm³). In addition, the system contains SnSe-based solid solutions, Sn_{1 ? x} Dy _x Se (up to 4 mol % DySe). Their electrical conductivity and thermoelectric power have been measured as functions of temperature.