Preparation and phase transition of Gd4(Al1 − xGax)2O9 solid solutions

The solid-solution compounds of Gd₄(Al_{1 – x} Ga _x )₂O₉ (x = 0.0–1.0) were prepared at 1600°C for 5 h in air. The unit cell volume of the compounds increased from 0.853 to 0.878 nm³ with x. Phase transitions having a temperature hysteresis were observed from 1100° to 1400°C by calorimetry and dilatometry. The transition temperature increased with x. The volume of the high-temperature phase was 0.5% smaller than that of the low-temperature phase at the transition temperature. The volume changes were independent of x. The hysteresis width observed by the dilatometry was about 300°C for the Gd₄Al₂O₉ ceramics (grain size: about 1 m) and decreased to 50°C for the Gd₄(Al_0.2Ga_0.8)₂O₉ ceramics (grain size: over 10 m). Gd₄Ga₂O₉ was unstable at low temperature and decomposed to Gd₃GaO₆ and Gd₃Ga₅O₁₂ during the thermal analyses.     

(Sr1−xCax)WO4 and (Sr1−xCax)WO4:Eu3+ nanoparticles: synthesis and luminescence

(Sr_1?xCa_x)WO₄ and (Sr_1?xCa_x)WO₄:0.05Eu³⁺ nanoparticles were synthesized by precipitation without using any complexing agent. The XRD patterns show that the obtained samples present a scheelite-type tetragonal structure without deleterious phase, and the increase of Ca concentration decreases the cell volume of materials. The TGA/DTA curve shows that the materials began to crystallize at temperature of 650 °C. The excitation and emission spectra of (Sr_1?xCa_x)WO₄ samples show bands originating from the charge transfers within WO₄ ^2? groups. All (Sr_1?xCa_x)WO₄ samples show broad blue emission at room temperature. The excitation and emission spectra of (Sr_1?xCa_x)WO₄:0.05Eu³⁺ samples show bands originating from the charge transfers of Eu³⁺ ions. All (Sr_1?xCa_x)WO₄:0.05Eu³⁺ samples show prominent red emission at room temperature. The substitutions of Ca²⁺ ions to Sr²⁺ ions have obvious influence on luminescence properties. The intensity and quantum efficiency increase with the substituted Ca concentrations.     

Synthesis and IR-excited luminescence of (Y1 − x Tm x )2O2S solid solutions

We have studied the key features of the luminescence spectra and kinetics of (Y_{1 ? x} Tm _x )₂O₂S solid solutions in the range 400–2000 nm under laser excitation at 790 and 810 nm. The results have been used to develop a series of IR phosphors “invisible” under laser excitation in the range 790–810 nm and possessing tunable and reproducible relative intensities of three groups of IR luminescence bands in the ranges 770–840, 1360–1520, and 1650–1980 nm, respectively.     

Decomposition of (Sn2xFe1−xSb1−x)O4 solid solutions with x≤0.50

Thermal stabilities of the rutile-type (Sn_2xFe_1−xSb_1−x)O₄ solid solutions with x≤0.5 were investigated by TG–DTA in flowing O₂ up to 1673 K. After thermal analysis the samples were characterised by means of powder X-ray diffraction analysis (XRD), optical and scanning electron microscopy (SEM) observation and electron dispersive spectrometry (EDS) analysis. The decomposition of the solid solution involves the formation of hematite and a volatile Sb oxide, probably Sb₄O₆. The decomposition temperature increases with the Sn content of the solid solution.     

Synthesis and properties of LiZr2(AsO4)3 and LiZr2(AsO4) x (PO4)3 − x

The LiZr₂(AsO₄)₃ arsenate and LiZr₂(AsO₄) _x (PO₄)_{3 ? x} solid solutions have been prepared through precipitation followed by heat treatment, and characterized by X-ray diffraction, X-ray structure analysis, IR spectroscopy, and impedance spectroscopy. We have established conditions for the crystallization of the arsenate and a continuous series of arsenate phosphate solid solutions (0 ≤ x ≤ 3), which have been obtained as two polymorphs: monoclinic and hexagonal. Using the Rietveld method, we have refined the crystal structures of the polymorphs of LiZr₂(AsO₄)₃ (sp. gr. P2₁/n, a = 9.1064(2), b = 9.1906(2), c = 12.7269(3) Å, β = 90.844(2)°, V =1065.03(5) ų, Z = 4; sp. gr. R $\bar 3$ c, a = 9.1600(4), c = 22.9059(13) Å, V = 1664.44(14) Å, Z = 6) and LiZr₂(AsO₄)_1.5(PO₄)_1.5. Their structural frameworks are built up of AsO₄ tetrahedra—or (As,P)O₄ tetrahedra occupied by arsenic and phosphorus atoms at random—and ZrO₆ octahedra, with the lithium atoms in between. The ionic conductivity of the materials has been measured. The cation conductivity of monoclinic LiZr₂(AsO₄) _x (PO₄)_{3 ? x} with 0 ≤ x ≤ 1 has been shown to exceed the conductivity of lithium zirconium phosphate.     

Electronic conductivity of Sr3-3xLa2x█x(VO4)2 solid solutions

The electronic conductivity of Sr_3-3xLa_2x█_x(VO₄)₂ solid solutions was measured at oxygen pressures from 10^-13 to 10⁵ Pa and temperatures from 1070 to 1270 K, and their band gap was determined as a function of composition. The activation energy (≏2.85 eV) and enthalpies of electron generation (≏4.2 eV) and migration (≏0.75 eV) were determined. A correlation between the band gap and electronic conductivity of the solid solutions was revealed     

δ-FeO(OH) and its solid solutions

A transmission electron microscope imaging investigation was performed on small -FeO(OH) crystallites less than 50 Å thick and several hundred angstroms across. We have observed faceting, and a hexagonal plate-like morphology with topological features near atomic step heights. Because of the mutual magnetic attraction on these particles, they tend to align with their thin direction (c-axis) either parallel or perpendicular to the support film surface. It is therefore possible to view dislocations or buckling of lattice planes of these plates either edge-on or perpendicular to this direction by direct lattice imaging in both the bright-field and dark-field modes. A highly distorted lattice is apparent when viewing the particles edge-on, and it is possible to show lattice projections to a resolution of 2.1 Å.     

δ-FeO(OH) and its solid solutions

-FeO(OH)-type solid solutions have been synthesized with compositions Fe_1–x M _x O_1–x (OH)_1+x ranging up tox=0.10 for M=Ca,x=0.35 for M=Mg or Cd andx=0.40 for M=Zn. The phases are characterized by X-ray diffraction and transmission electron microscope studies. A structural model giving satisfactory intensity agreement is postulated for Fe_1–x Zn _x O_1–x (OH)_1+x . In this model, Zn²⁺ ions are situated in the 0 0 0 octahedral sites of space group D _3d ³ -P¯3ml while the Fe³⁺ ions are almost equally distributed among both octahedral sites (0 0 0 and 0 0 1/2).     

Formation and characterization of the solid solutions (CrxFe1−x)2O3, 0⩽x⩽1

The solid solutions (Cr_xFe_1–x)₂O₃, 0 x 1, were prepared by traditional ceramic procedures. The samples were characterized using X-ray diffraction, Mössbauer, Fourier transform infra-red (FT-IR) and optical spectroscopic measurements. In the whole concentration range two phases exist phase F, -(Cr_xFe_1–x)₂O₃, which is isostructural with -Fe₂O₃ and phase C, which is closely related to Cr₂O₃. Phase F exists in samples heated up to 900°C, for 0 x 0.95. Phase C exists from x0.27 to x=1 for samples heated up to 900°C and from x0.65 to x=1 for samples heated up to 1200 °C. For samples heated up to 900 °C, the solubility limits were 27.5 ± 0.5 mol% of Cr₂O₃ in -Fe₂O₃ and 4.0 ± 0.5 mol % of -Fe₂O₃ in Cr₂O₃. For the samples heated at 1200 °C the diffraction peaks for the F and C phases in the two phase region were severely overlapped and thus the solubility limits could not be determined accurately as for previous samples. ⁵⁷Fe Mössbauer spectra of the samples heated up to 1200 °C showed significant broadening of spectral lines and a gradual decrease of the hyperfine magnetic field with increase of x up to 0.50. For x0.7, a paramagnetic doublet with collapsing sextet was observed. The spectra were interpreted in terms of an electronic relaxation effect; however, an agglomeration of iron ions which would contribute to the superparamagnetic effect could not be excluded. The FT-IR spectra showed transition effects in accordance with the X-ray diffraction results. The most intense absorption bands, observed for the samples heated up to 1200 °C, were located at 460 and 370 nm (22 000 and 27 000cm^–1) for x 0.5, 500 and 360 nm for x < 0.3, and might be correlated with the strong enhancement of the pair transitions through antiferromagnetic interactions. The intensification of the ⁶A₁ 4T₁ Fe³⁺ ions in all spectra and the development of the absorption at 13000 cm^–1 due to a metal-metal charge transfer (Cr³⁺ Fe³⁺) transition, might be explained by exchange coupling which has been observed in some spinel compounds.     

Scandium and gallium substitution effects in the (Y1−xScx)Ba2Cu4O8 and (Y1−xGax)Ba2Cu4O8 superconducting oxides

In this study scandium and gallium substitution effects in the YBa₂Cu₄O₈ (Y-124) superconducting cuprate have been investigated. The superconducting (Y_1?xSc_x)Ba₂Cu₄O₈ and (Y_1?xGa_x)Ba₂Cu₄O₈ (x = 0.0, 0.05, 0.1 and 0.2) compounds have been synthesized using a simple sol–gel synthesis technique. The obtained oxides were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TG) and resistivity measurements. The X-ray diffraction patterns of the samples with x = 0.0, 0.05, and 0.1 showed that the single phase (Y_1?xSc_x)Ba₂Cu₄O₈ and (Y_1?xGa_x)Ba₂Cu₄O₈ compounds have formed. Moreover, the XRD results are completely supported by TG measurements. The results of resistivity measurements for the (Y_1?xSc_x)Ba₂Cu₄O₈ samples showed that the onset critical temperature of superconductivity for these samples slightly increased. Contrarily, T_C for the (Y_1?xGa_x)Ba₂Cu₄O₈ samples decreased monotonically with the increasing amount of gallium.     

Defect structure of xY2O3 · (1 − x)TiO2 (x = 0.5–0.58) solid solutions

X-ray diffraction characterization with monochromatic synchrotron X-rays has demonstrated that xY₂O₃ · (1 ? x)TiO₂ (x = 0.5–0.58) solid solutions consist of a fluorite-like (Fm3m) disordered phase and a nanoscale (?40–1000 nm) pyrochlore-like (Fd3m) ordered phase of the same composition, coherent with the disordered phase. In the composition range of the solid solutions (0.5 ≤ x ≤ 0.58), the lattice parameter of the fluorite-like phase follows Vegard’s law. The formation of nanodomains with different degrees of order is shown to be caused by the internal strain due to the high density of structural defects in their unit cells. The materials obtained in this study possess enhanced sorption capacity and can be used as catalysts, catalyst supports, gas sensors, etc.     

Preparation and X-ray diffraction, dielectric, and Mössbauer characterization of Co1 − x Ni x Cr2O4 solid solutions

Co_{1 ? x} Ni _x Cr₂O (0 ≤ x ≤ 1) ceramic samples have been characterized by X-ray diffraction and relative dielectric permittivity ?(T), loss tangent tan δ(T) (0.1–200 kHz), and thermally stimulated depolarization current (TSDC) measurements in the range 100–350 K. The samples were shown to consist of spinel solid solutions with a cubic (0 < x ≤ 0.98) or tetragonal (0.99 ≤ x < 1) structure. Increasing the Ni content of the samples from 0 to 100 at % increases their tanδ and 1/ρ by three to four orders of magnitude. The ?(T), tan δ(T), and TSDC of the samples with 0.2 ≤ x ≤ 0.6 have anomalies at T ₁ ～ 220 K and T ₂ ～ 240 K, which point to a transition to a polar state below T ₂. Samples containing 1–4 at % ⁵⁷Fe as an impurity were characterized by Mössbauer spectroscopy in the range 54–330 K and were shown to be magnetically ordered at 78 K. We conclude that the solid solutions have ferroelectric properties with a Curie temperature T ₂ and magnetoelectric multiferroic properties.     

Structure and properties of (1 − x)BiFeO3 · xPbFe2/3W1/3O3 (0 ≤ x ≤ 1) solid solutions

(1 ? x)BiFeO₃ · xPbFe_2/3W_1/3O₃ ((1 ? x)BFO · xPFWO) samples with 0 ≤ x ≤ 1 have been prepared by a standard ceramic processing technique and characterized by X-ray diffraction, dielectric measurements, and Mössbauer spectroscopy. The system has been shown to contain a continuous series of perovskite solid solutions. The solid solutions in the range 0 ≤ x < 0.32 have a rhombohedral structure and those with 0.32 ≤ x ≤ 1 have a cubic structure. Increasing the BFO content from 0 to 40% leads to rapid degradation of the dielectric permittivity peak that occurs at 180 K in PFWO and is due to the relaxor behavior of this component. At higher BFO concentrations, the electrical conductivity of the solid solutions increases by about two orders of magnitude. The temperature dependences of permittivity for the samples containing ～80% BFO have prominent maxima around 430 and 520 K, whose position is frequency-independent. The solid solutions exhibited no piezoelectric or pyroelectric effect, probably because they were insufficiently poled in a field of 10 kV/cm at 300 K. At higher electric field intensities, the samples experienced breakdown.     

Synthesis and properties of TlIn1 − x Gd x Se2 solid solutions

This paper describes the synthesis and crystal growth of TlIn_{1 − x} Gd _x Se₂ solid solutions and presents the T-x phase diagram of the TlInSe₂-TlGdSe₂ system. Partial gadolinium substitution for indium in TlInSe₂ increases the microhardness and unit-cell parameters of the material and reduces its band gap. According to X-ray diffraction data for TlInSe₂-TlGdSe₂ crystals, the TlIn_{1 − x} Gd _x Se₂ (0 < x ≤ 0.1) solid solutions crystallize in tetragonal symmetry and are isostructural with TlInSe₂.     

CuCr2–xSbxS4 and Cu1–ySbyCr2S4 solid solutions

CuCr_2–ySb_xS₄ and Cu_1–ySb_yCr₂S₄ solid solutions with the spinel structure were synthesized, and their magnetic and electrical properties were studied. The limits of solid solutions in these systems were found to bex = 0.5 andy = 0.22. Models of the cation distributions in the solid solutions are proposed. The CuCr_2-xSb_xS₄ solid solutions with 0.10 <x < 0.15 are magnetic semiconductors with high ferromagnetic ordering temperatures.     

Metastability of the K2NiF4 type structure of the solid solution LaCa(Cr x Al1−x )O4(0⩽x⩽0.10)

Metastability of the K₂NiF₄ type aluminate LaCaAlO₄ and its chromium diluted solid solution LaCaCr _x Al_1–x O₄ (x0.10) was evidenced at 1400C in air, in terms of demixing into the parent structures of the 11 intergrowth, i.e. the perovskite and rocksalt type LaAlO₃ (LaCr _x Al_1–x O₃) and CaO, respectively. This behaviour is discussed comparatively with YCaAlCO₄ and LaSrAlO₄ whose structures are stable under the same thermodynamic conditions. The results of a structure analysis are used to emphasize the role of the nine-fold co-ordination of the (A ³⁺=Y³⁺, La³⁺; A²⁺=Ca²⁺, Sr²⁺) cations as mixing the twelve-fold co-ordination of A ³⁺ in A ³⁺AlO₃ perovskite and the six-fold one of A ²⁺ in A ²⁺O rocksalt. Calcium-oxygen underbonding in the (La, Ca)-O-Al bridge is assumed to trigger the metastability of the intergrowth structure at high temperature.     

射频磁控溅射法制备Al2(WO4)3薄膜和负热膨胀性能研究

采用WO3和Al2O3陶瓷靶材,以双靶交替射频磁控溅射法,在石英基片上沉积制备了Al2（WO4）3薄膜。利用X射线衍射仪（XRD）、扫描电子显微镜（SEM）,研究了退火温度对Al2（WO4）3薄膜的相组成和表面形貌的影响,采用表面粗糙轮廓仪和划痕仪测量薄膜厚度,探索了薄膜的制备工艺以及薄膜与基片的结合力,采用高温X射线衍射和晶胞参数指标化软件,初步研究了薄膜热膨胀特性。实验结果表明：磁控溅射沉积制备的这种薄膜为非晶态,表面平滑、致密,随着热处理温度的升高,薄膜开始结晶且膜层颗粒增大,在950℃热处理10min后得到Al2（WO4）3薄膜,薄膜与基片的结合力为13．6N,薄膜物质热膨胀特性呈各向异性。     

Thermal studies of Cr2O3 doped CaCO3-SiO2 (2∶1) system

Mixtures of CaCO₃SiO₂ in 21 molar ratio were subjected separated to thermal analysis with varying concentration of Cr₂O₃ (0.1 to 5%) as dopant. The activation energy (E _a) and enthalpy (H) shows a decreasing trend with 0.1 to 1% Cr₂O₃ and attains a minimum value with 1% dopant. 0.1 to 0.5% Cr₂O₃ helps in the formation of and C₂S, (Cement Chemistry notations, C = CaO, S = SiO₂) phases at 1400° C and above but 1% Cr₂O₃ stabilizes -C₂S phase along with a little free lime and CaCrO₄. A small quantity of CaCrO₄, Cr₂SiO₂ and -C₂S are also formed along with the major phases with 5% Cr₂O₃ indicating that Cr³⁺ can substitute both Ca²⁺ and Si⁴⁺ ions in the C₂S lattice.