Subsolidus phase relations of the SrO–Ta2O5–CuO system at 900 °C in air

The subsolidus phase relations of the SrO–Ta₂O₅–CuO system were investigated in air. The samples were equilibrated at 900 °C. The ternary oxide Sr₃Ta₂CuO₉ compound is stable under these conditions. This phase presents a solid solution range, its actual composition being Sr₃Ta_2−xCu_1+xO_9+δ with 0.0 ≤ x ≤ 0.2. Up to about 5 at.% Cu can be incorporated in the Sr_3−xTa_1+xO_5.5+δ phase. Similarities with the SrO–Nb₂O₅–CuO system are discussed.     

Phase relations in the SrO–Ga2O3–B2O3 system

The subsolidus phase relations in the SrO–Ga₂O₃–B₂O₃ system were investigated. The system contains 10 binary compounds and two ternary compounds, and can be divided into 15 three-phase regions. The new ternary compound SrGaBO₄ has two modifications (- and β-phases), both of which crystallize in the orthorhombic system but with different space groups.     

Multiwavelength excited novel red-emitting phosphor Eu-activated Li2Zn2(MoO4)3

Eu³⁺-activated Li₂Zn₂(MoO₄)₃ multiwavelength excited red-emitting phosphors were synthesized via a solid state reaction. The structure and photoluminescence characteristics were investigated by X-ray powder diffraction and fluorescent spectrophotometry, respectively. The excitation spectrum included a strong broadband ranging from 250 to 350 nm and some sharp peaks at 363, 384, 395, 465, and 533 nm, which matchs the radiations of near-UV or blue light-emitting diodes chip well. Upon excitation either of near-UV or blue even green light, the intense red emission with 615 nm peak can be observed, which is ascribed to the ⁵D₀-⁷F₂ transition of Eu³⁺ ions. The chromaticity coordinates (x = 0.65, y = 0.34) of the as-obtained phosphor is very close to the National Television Standard Committee standard values (x = 0.67, y = 0.33). All these characteristics suggest that Eu³⁺-doped Li₂Zn₂(MoO₄)₃ wavelength-conversion material to be suitable candidate red component for phosphor-converted white light-emitting diodes.     

Bulk and lattice thermal expansion in Ce1−xSrxO2−x (0.0≤x≤0.10)

In this communication, we report on the bulk and lattice thermal expansion studies on a number of compounds, within the homogeneity range of solid solutions, in a series with the general composition Ce_1−xSr_xO_2−x (0.0≤x≤0.10). The XRD pattern of each product was refined to determine the solid solubility of SrO into the lattice of CeO₂, and the homogeneity range. The composition with maximum solid solubility limit of SrO in CeO₂ lattice, under the slow cooled conditions, was delineated as Ce_0.91Sr_0.09O_1.91 (i.e. 9 mol.% of SrO). The bulk thermal expansion measurements from ambient to 1123 K, as investigated by a dilatometer, revealed that the _l (293 to 1123 K) values for the compositions within the homogeneity range increase from 11.58×10⁻⁶ to 12.13×10⁻⁶ K⁻¹ on increasing the Sr²⁺ content from 0 mol.% (i.e. CeO₂) to 9 mol.%, i.e. the upper solubility limit of SrO into the lattice of CeO₂. A similar trend was observed in the lattice thermal expansion coefficients _a (293 to 1473 K) as obtained by a high temperature-XRD.     

Investigation of the Y2Te3–Cu2Te–PbTe system at 870 K and crystal structures of the Y7Cu3Te12 and YCu0.264Te2 compounds

The structural and magnetic properties of doubly substituted Nd₂Fe_17−x−yTi_xGa_y (0 ≤ x ≤ 1.0, 0 ≤ y ≤ 3) compounds have been investigated by a combined technique of X-ray diffraction, neutron diffraction and magnetic measurements. Rietveld refinements of the diffraction data indicate that all the samples crystallize in the rhombohedral Th₂Zn₁₇-type structure. For a given Ti content (x), the lattice parameters a and c, and unit cell volume V of Nd₂Fe_17−x−yTi_xGa_y all increase linearly with increasing Ga content. The addition of Ti initially has a considerably positive effect on the increasing rates of a, c, and unit cell volume V, but later the effect becomes very slight and even negative with the further increase of Ti content. The site occupancies of Ti and Ga in the crystallographic sites change a little compared to what is observed in the corresponding singly substituted compounds. The effects of Ti and Ga on the bond lengths of the doubly substituted compounds are quite different from that of the singly substituted compounds. Magnetic measurements show the T_C of Nd₂Fe_17−x−yTi_xGa_y increases with increasing Ti content for a low Ga content while it behaves conversely for a higher Ga content. The T_C of Nd₂Fe_17−x−yTi_xGa_y increases with increasing Ga content for a particular Ti content, while the addition of Ti results in a slower increase of T_C on the Ga content (y ≤ 3). For a given Ti content, the M_s of Nd₂Fe_17−x−yTi_xGa_y first increases a little and then decreases with the increase of Ga content, while for a given Ga content the M_s of Nd₂Fe_17−x−yTi_xGa_y decreases with the increase of Ti content.     

Mechanism of the α-to-β phase transformation in the LaNi5-H2 system

High-energy synchrotron in situ X-ray powder diffraction has been used to elucidate the mechanism of the hydriding phase transformation in a LaNi₅ model hydrogen storage intermetallic in real time. The transformation proceeds at 10 °C via the transient growth of an interfacial phase, the γ phase, with lattice parameters intermediate between those of the α (dilute solid solution) and β (concentrated hydride) phases. The γ phase forms to partially accommodate the 24% change in unit cell volume between the α and β phases during hydriding and dehydriding. The α, γ and β phases coexist at the nanoscopic level.     

Phase diagram of the CsBr-CaBr2 system

The phase diagram of the CsBr-CaBr2 system was re-determined by using differential thermal analysis and high ternperature and room ternperature X-ray diffraction analysis. It is concluded that there are three intermediate compounds in this system： a.congruently melting compound, CsCaBr3, with a melting point of 823℃ and two incongruently melting compounds, Cs2CaBr4 and Cs3Ca2Br7, whose peritectic points being 597℃ and 635℃, respectively. X-ray diffraction analysis indicated that compound CsCaBr3 is of slightly distorted perovskite structure.     

Materials with layered structures X: subsolidus phase diagram of the system FeIn2S4–FeIn2Se4

The system (1−x)FeIn₂S₄–xFeIn₂Se₄ has been investigated by X-ray powder methods. The subsolidus phase diagram is constructed in the temperature interval 600–1000°C. The spinel type FeIn₂S₄ exhibits a phase width up to the composition FeIn₂S₃Se and the layered FeIn₂Se₄ is formed for 1≥x≥0.65. A new layered compound is formed for 0.55≥x≥0.4 which crystallizes at temperatures below 850°C in an -FeGa₂S₄ structure with a=363.6 pm and c=1207.1 pm (x=0.5) for the hexagonal cell and at higher temperatures in the MgAl₂S₄-type with a=393.9 pm and c=3843.2 pm (x=0.5) for the hexagonal cell. Both structures have been refined by the Rietveld-method. All phase boundaries are nearly independent from temperature.     

Thermal behavior of the amorphous precursors of the ZrO2–GaO1.5 system

The amorphous precursors of the ZrO₂–GaO_1.5 system on the ZrO₂-rich side of the concentration range were prepared by co-precipitation from aqueous solutions of the corresponding salts. Thermal behavior of the amorphous precursors was monitored using differential thermal analysis (DTA), X-ray powder diffraction (XRD), Raman spectroscopy and field emission scanning electron microscopy (FE-SEM). Crystallization temperature of the amorphous precursors rose with an increase in the GaO_1.5 content, from 405 °C (0 mol% GaO_1.5) to 720 °C (50 mol% GaO_1.5). The results of Rietveld refinements indicated that the maximum solubility of Ga³⁺ ions in the ZrO₂ lattice (43 mol%) occurred in the metastable products obtained after crystallization of the amorphous precursors. Further thermal treatment caused a decrease of the solubility limits, which became negligible after calcination at 1100 °C. The results of Raman spectroscopy showed that the incorporation of Ga³⁺ ions partially stabilized the tetragonal polymorph of ZrO₂, but could not stabilize its cubic polymorph. The incorporation of Ga³⁺ ions caused a linear decrease in the unit-cell volume of the ZrO₂-type solid solutions, but the rate of the decrease turned out to be smaller than the rate obtained after the incorporation of bigger Fe³⁺ ions.     

Phase diagram of the CuGaSe2–SiSe2 and CuInSe2–SiSe2 systems

The phase diagrams of the CuGaSe₂–SiSe₂ and CuInSe₂–SiSe₂ systems were constructed using the results of differential thermal and X-ray phase analysis. Both systems are of the eutectic type with the eutectic point coordinates 75 mol% SiSe₂, 1042 K (CuGaSe₂–SiSe₂); 67 mol% SiSe₂, 1083 K (CuInSe₂–SiSe₂). Solid solutions based on CuGaSe₂ and CuInSe₂ were discovered in these systems; their extent at 670 K being 24 and 25 mol% SiSe₂, respectively. The crystal structure of the limiting compositions of these solid solutions was refined.     

Synthesis, structure, and properties of Li2Pb2CuB4O10 with isolated [CuB4O10] units

The copper borate Li₂Pb₂CuB₄O₁₀ has been synthesized in air by the standard solid-state reaction at temperature in the range 550-650 °C and the structure of Li₂Pb₂CuB₄O₁₀ was determined by single-crystal X-ray diffraction. Li₂Pb₂CuB₄O₁₀ crystallizes in the monoclinic space group C2/c (no. 15) with a = 16.8419(12), b = 4.7895(4), c = 13.8976(10) Å, and β = 125.3620(10)°, V = 914.22(12) Å³, and Z = 4, as determined by single-crystal X-ray diffraction. The Li₂Pb₂CuB₄O₁₀ structure exhibits isolated units of stoichiometry [CuB₄O₁₀]⁶⁻ that are built from CuO₄ distorted square planes and triangular BO₃ groups. The IR spectroscopy and thermal analysis investigations of Li₂Pb₂CuB₄O₁₀ are also presented.     

Room temperature multiferroicity in Bi rich Fe deficient Gd doped Bi1.2Gd0.1Fe0.8O3

A clean signature of room temperature multiferroicity in Bi_1.2Gd_0.1Fe_0.8O₃ ceramics is observed. Samples were prepared by slow step sintering technique at 850 °C. Impurity peaks normally present in original BiFeO₃ are completely suppressed with the increase of Bi concentration. Apart from this, structural transformation took place from R3_C to Pn2₁a space group and a clear orthorhombic grain growth habit is seen by SEM microstructure. Suppression of impurity phases favors the reduction of mobile oxygen vacancies and hence reduces leakage current for which ferroelectric properties of Bi_1.2Gd_0.1Fe_0.8O₃ are enhanced. We argue that the addition of Gd is likely to suppress the spiral spin modulation and at the same time increase the canting angle which favors the enhanced ferromagnetism. Excess Bi is expected to act as point defects and occupy interstitial positions which in turn surrounded by oxygen vacancies and is likely to promote defect driven ferromagnetism with enhanced spin and electric polarization. This finding encourages further revaluation of long-discounted BiFeO₃ for multiferroics research.     

Subsolidus phase relation in the system ZnO–Li2O–MoO3

The subsolidus phase relation of the system ZnO–Li₂O–MoO₃ has been investigated by X-ray diffraction (XRD) analyses. The phase diagram has been constructed. There are six binary compounds and one ternary compound in this system. The phase diagram comprises nine three-phase regions. The ternary compound Li₂Zn₂(MoO₄)₃ is refined by the Rietveld method. It belongs to an orthorhombic system with space group Pnma and lattice constants a = 5.1114 Å, b = 10.4906 Å, c = 17.6172 Å.     

Solubility of YbTe in Sb2Te3 and thermodynamic properties of the solid solution

The solubility of YbTe in Sb₂Te₃ is investigated by a combination of DTA, XRD, SEM, and EMF methods. The fragment of the T-x phase diagram of the YbTe-Sb₂Te₃ system is constructed for 0-25 mol.% YbTe. It is shown that the solubility limit for YbTe in Sb₂Te₃ is achieved at 15 mol.% YbTe at 300 K and at 17.5 mol.% YbTe at 855 K. From the EMF measurements with an YbTe electrode the partial thermodynamic functions of the YbTe pseudo-component are calculated for the alloys of different compositions. Also, the standard integral thermodynamic functions of the YbTe dissolution in Sb₂Te₃ as well as the standard thermodynamic functions of formation and the standard entropy of the solid solution are calculated from the experimental data.     

Crystal structure of Nax(MoO)5(P2O7)4 studied by synchrotron X-ray diffraction

The crystal structure of sodium pentamolybdyl tetradiphosphate Na_x(MoO)₅(P₂O₇)₄ has been determined from synchrotron diffraction data collected at 293 K on two microcrystals. The compound crystallizes in a monoclinic space group I 1 1 2/a (no. 15, setting 11), with unit cell parameters a = 22.905(3), b = 23.069(2), c = 4.8537(2) Å, γ = 90.641(9)° and a = 22.898(3), b = 23.056(2), c = 4.8551(2) Å, γ = 90.82(1)°, for crystals I and II, respectively. The structure is pseudo-tetragonal, and the crystals are pseudo-merohedrally twinned by 90° rotation around the c-axis. The structure closely resembles the previously reported Li-deintercalated Mo_1.3OP₂O₇ [V.V. Lisnyak, N.V. Stus, P. Popovich, D.A. Stratiychuk, Ya. Filinchuk, V.M. Davydov, J. Alloys Compd. 360 (2003) 81–84]. Comparison of the two structures led us to conclude that the Mo₂ and Mo₃ clusters were erroneously identified in Mo_1.3OP₂O₇. A revised structure of Mo_1.3OP₂O₇ contains a fully occupied oxygen site instead of the 16% occupied Mo(2) site, thus the revised formulae for the Li-deintercalated compound is (MoO)₅(P₂O₇)₄. In both structures, the (MoO)₅(P₂O₇)₄ framework strongly resembles the one in the earlier reported Ag(MoO)₅(P₂O₇)₄, while the location of Na and Ag atoms differ.     

Synthesis of novel rare earth—Iron oxide chalcogenides with the La2Fe2O3Se2 structure

Our searches for new oxide chalcogenides of rare earths and Fe, Co, Ni, and Zn resulted in preparation of two new compounds Ce₂Fe₂O₃S₂ and Pr₂Fe₂O₃S₂ which are isostructural to La₂Fe₂O₃Se₂ and Sm₂Ti₂O₃Sb₂. Crystal structures of the new compounds Ce₂Fe₂O₃S₂ and Pr₂Fe₂O₃S₂ were determined from powder X-ray diffraction data. Magnetic measurements were performed for Ce₂Fe₂O₃S₂ and revealed behavior very similar to that of isostructural oxide chalcogenides of iron and pnictides of titanium. In particular, no superconductivity was observed down to 4 K. Crystal chemical factors determining the stability of the La₂Fe₂O₃Se₂ structure type are discussed.     

Crystal structure of La5Ti4GaO17

The crystal structure of La₅Ti₄GaO₁₇ compound synthesized by heat-treatment of the co-precipitated hydroxy-oxalates has been determined by the X-ray powder diffraction. It was found that crystal structure of La₅Ti₄GaO₁₇ belongs to the CaLa₄Ti₅O₁₇-type structure (space group Pmnn, a = 0.3912(1) nm, b = 3.128(1) nm, c = 0.5523(1) nm, Z = 2). The final R_W value is equal to 0.081 for 169 independent reflections.     

Combustion synthesis of TiC–TiB2 composites

An experimental study on formation of TiC–TiB₂ in situ composites with a broad range of compositions was conducted by self-propagating high-temperature synthesis (SHS) using the reactant compacts from different combinations of Ti, B₄C, C, and B powders. Direct reaction of Ti with B₄C at stoichiometry of Ti:B₄C = 3:1 yields a TiB₂-rich composite with TiC:TiB₂ = 1:2. Formation of the products containing 20, 33.3, and 50 mol% of TiB₂ was achieved by the Ti–B₄C–C reactants. In addition, the test specimen composed of Ti, B₄C, and B was employed for the synthesis of a composite with 80 mol% TiB₂. Among three different types of the powder compacts, the boron-containing sample was characterized by the fastest combustion wave and the highest reaction temperature. The lowest combustion temperature and wave velocity were observed in the Ti–B₄C compact. When fine Ni particles were added to the Ti–B₄C reactant, it was found that the propagation rate of the reaction front was increased and the densification of the end product was enhanced significantly. This was attributed to formation of the Ti–Ni eutectic liquid during the reaction. As a result, the relative density of a TiC + 2TiB₂ composite increases from 30 to 86% with the Ni content from 0 to 20 mol%. Based upon the XRD analysis, small amounts of TiNi₃ and TiB were detected in the Ni-reinforced TiC–TiB₂ composites.     

Reactions in the SrH2–Al–H2 system

Five rare-earth R₅CoSb₂ antimonides have been synthesized and characterized by means of X-ray powder diffraction data. The investigated ternary compounds crystallize with orthorhombic ordered substituted variant of the Yb₅Sb₃ structure type (space group Pnma, Pearson symbol oP32). Atomic and thermal parameters have been refined for all intermetallic phases.