Hexagonal Solid Solution Research Articles

An electrochemical study on the influence of sodium molybdate on electrodeposition process and phase composition of ternary Zn–Ni–Mo alloy coatings

Ternary Zn–Ni–Mo alloy coatings were deposited from a citrate-sulphate bath at pH 5.7 containing different amounts of sodium molybdate. The content of molybdenum in the coatings (from 0.3 to 5.2 at.-%) can be easily controlled by increasing sodium molybdate concentration in the plating bath from 0.0025 to 0.05 mol dm− 3, which results also in deposition of smoother deposits. An increase in molybdate concentration leads to the shift of reduction potentials towards more negative values and to the decrease in current efficiency of deposition process. XRD analyses and anodic linear sweep voltammetry (ALSV) measurements demonstrated that at least two phases are formed in the Zn–Ni–Mo alloy: a hexagonal zinc phase or solid solution of nickel in zinc and Ni5Zn21 intermetallic compound. Furthermore, the XRD analyses revealed a third phase, which could be assigned to the oxidised species of molybdenum or other alloying metals.

The plutonium–oxygen phase diagram in the 25–900 °C range: Non-existence of the PuO1.515 phase

Evaluation of data for phases formed in the Pu–O system at temperatures below 900°C shows that the observed oxides are not at equilibrium. Results are consistent with coexistence of a hexagonal solid solution (hex-PuO1.5+z, 0⩽z⩽0.010) and a cubic phase (cub-PuO1.60) in equilibrium at 800°C, but fail to confirm that the O/Pu ratio of the body-centered-cubic (bcc) oxide formed near the sesquioxide composition is 1.515 (1.52) or that bcc-PuO1.515 is formed by the peritectic reaction of hex-PuO1.510 with cub-PuO1.60. Stable Pu(IV)/Pu(III) ratios observed for products of the Pu–H2O reaction correspond to members of the PunO2n−2 homologous series, but a product is not formed at O/Pu=1.515. Metastable bcc-PuO1.50 (n=4) and stable hex-PuO1.5+z coexist below 285°C, the point at which reversible eutectic decomposition of cubic PuO1.60 (n=5) produces a non-equilibrium mixture of bcc-PuO1.50 and sub-stoichiometric dioxide (PuO2−y). Transformation of bcc-PuO1.50 to stable hex-PuO1.50 and reactions of the hexagonal oxide to form higher-composition cubic phases are kinetically hindered. An alternative diagram describing non-equilibrium chemical behavior of the Pu–O system is presented.

Formation of Bundle-Shaped β-NaYF4 Upconversion Microtubes via Ostwald Ripening

In this work, the uniform bundle-shaped microtubes composed of six half-pipes are synthesized for the first time in hydrothermal solutions via an intentional delayed phase transition pathway induced by Mn(2+) doping. The structural and kinetic factors that govern the phase and shape evolution of NaYF4 microcrystals have been carefully studied, and the influences of Mn(2+) to RE(3+) ratio, the amount of trisodium citrate, and the pH value in conjunction with the intrinsic character of RE(3+) ions on the phase and shape evolution are systematically discussed. It is found that the proper Mn(2+) to RE(3+) ratio is mainly responsible for delayed phase transition process and induces interior density gradient of solid aggregate for creating hollow bundle-shaped microtubes. While the amount of trisodium citrate and the pH value are the keys for the shape control of the NaYF4 microcrystals such as prismatic microtubes, prismatic short rods, thin plates, and particles. The up and downconversion emissions were obtained independent of whether α- or β-NaYF4:Er(3+)/Yb(3+) samples doped with Mn(2+), but the significant tuning of output color was only obtained in cube NaYF4 nanoparticles rather than in hexagonal microtubes via adjusting the amount of Mn(2+) ions. These spectral measurements and EDX analyses indicate that the distribution or concentration of Mn(2+) in hexagonal phase solid solution has changed, which supports Ostwald ripening growth mechanism and rules out agglomeration or oriented attachment growth mechanism. We designed crystal growth mode by simply addition of dopant may provide a versatile approach for fabricating a wide range of hollow nano/microcrystals and thus bring us a clearer understanding on the interaction between the dopant reagents and the nano/microcrystals.

Growth and thermal stability of (V,Al)2Cx thin films

Abstract

Phase Relationships in the BaO–Ga2O3–Ta2O5System and the Structure of Ba6Ga21TaO40

Phase relationships in the BaO-Ga(2)O(3)-Ta(2)O(5) ternary system at 1200 °C were determined. The A(6)B(10)O(30) tetragonal tungsten bronze (TTB) related solution in the BaO-Ta(2)O(5) subsystem dissolved up to ~11 mol % Ga(2)O(3), forming a ternary trapezoid-shaped TTB-related solid solution region defined by the BaTa(2)O(6), Ba(1.1)Ta(5)O(13.6), Ba(1.58)Ga(0.92)Ta(4.08)O(13.16), and Ba(6)GaTa(9)O(30) compositions in the BaO-Ga(2)O(3)-Ta(2)O(5) system. Two ternary phases Ba(6)Ga(21)TaO(40) and eight-layer twinned hexagonal perovskite solid solution Ba(8)Ga(4-x)Ta(4+0.6x)O(24) were confirmed in the BaO-Ga(2)O(3)-Ta(2)O(5) system. Ba(6)Ga(21)TaO(40) crystallized in a monoclinic cell of a = 15.9130(2) Å, b = 11.7309(1) Å, c = 5.13593(6) Å, β = 107.7893(9)°, and Z = 1 in space group C2/m. The structure of Ba(6)Ga(21)TaO(40) was solved by the charge flipping method, and it represents a three-dimensional (3D) mixed GaO(4) tetrahedral and GaO(6)/TaO(6) octahedral framework, forming mixed 1D 5/6-fold tunnels that accommodate the Ba cations along the c axis. The electrical property of Ba(6)Ga(21)TaO(40) was characterized by using ac impedance spectroscopy.

Ce3+/Tb3+ activated GdF3, KGdF4, and CeF3 submicro/nanocrystals: Synthesis, phase evolution, and optical properties

Abstract

Bromide substitution in lithium borohydride, LiBH 4–LiBr

By means of in situ synchrotron radiation powder X-ray diffraction, powder neutron diffraction, attenuated total reflectance infrared spectroscopy, differential scanning calorimetry and the Sieverts techniques we have investigated how anion substitution in the LiBH 4–LiBr system leads to changes in the structural, physical, chemical and hydrogen storage properties of this material. Mechano-chemical treatment facilitates formation of a hexagonal solid solution h-Li(BH 4) 1−xBr x whereas heating at elevated temperatures, i.e. T > 112 °C appears to allow full solubility in the system LiBH 4−LiBr. The first step in the anion substitution process may be dissolution of small amounts of LiBH 4 in α-LiBr deduced from observation of a hexagonal solid solution with unit cell volume similar to β-LiBr for a hand-mixed sample. The solid solution, Li(BH 4) 1−xBr x, is isostructural to the hexagonal high temperature polymorph of LiBH 4. This solid solution melts at a significantly higher temperature depending on the composition as compared to h-LiBH 4. Furthermore, a new hexalithium borate tribromide, Li 6(BO 3)Br 3 was discovered and structurally characterized.

(Gd<sub>0.95</sub>Eu<sub>0.05</sub>)(OH)<sub>3</sub> Nanomaterials via Hydrothermal Processing and their Transformation into Single Crystalline (Gd<sub>0.95</sub>Eu<sub>0.05</sub>)<sub>2</sub>O<sub>3</sub> with Enhanced Photoluminescence

In this work, hexagonal solid solutions of (Gd0.95Eu0.05)(OH)3with two distinctive morphologies of nanorods and nanotubes were successfully synthesized via hydrothermal treatment of mixed nitrate solutions in the presence of ammonium hydroxide. The hydroxide samples exhibited characteristic Eu3+photoluminescence through the energy transfer from Gd3+to Eu3+and the self-excitation of Eu3+. The hydroxide precursors transformed into cubic (Gd0.95Eu0.05)2O3at ~500 °C via an intermediate monoclinic (Gd0.95Eu0.05)OOH phase, and the Eu3+coordination accordingly experienced symmetry changes fromD3htoC2v, and then toC2/S6. The cubic (Gd0.95Eu0.05)2O3well retained the original morphologies of their polycrystalline precursors and exhibited a single-crystalline character at 1000 °C. Greatly enhanced photoluminescence (~5000 times that of the hydroxides) was observed for the phase conversion.

Silicon Location in Silicate-Substituted Calcium Phosphate Ceramics Determined by Neutron Diffraction

The silicate incorporation in calcium phosphate bioceramics was studied by X-ray and neutron powder diffraction (joint Rietveld refinement) and micro-Raman spectroscopy. For a phosphate substitution level of 15 mol % multiphase ceramic is obtained passing from biphasic calcium phosphate (BCP) ceramic to ceramic composed of hydroxyapatite (HAp), silicocarnotite, and tricalcium phosphate (both α- and β-TCP polymorphs). The quantity of silicate incorporation increases when passing from β-TCP (Ca3(PO4)2, silicate level not measurable) to α-TCP (Ca3(PO4)1.875(SiO4)0.125 with 6.25 mol % of phosphate substitution or 1.13 wt % of incorporated silicon), to HAp (Ca10(PO4)4.9(2)(SiO4)1.1(2)(OH)1.0(1)O0.66(7) with 18.3 mol % of phosphate substitution or 3.11 wt % of silicon), and to silicocarnotite (Ca5(PO4)1.9(2)(SiO4)1.1(2) with 36.7 mol % of phosphate substitution or 6.40 wt % of silicon). The mechanism of silicate incorporation into HAp structure is multiple and involves the creation of two kinds of vacancies: hydroxyl vacancies and phosphate/silicate vacancies due to a carbonate-involving mechanism leading to the composition Ca10(PO4)6–x−2y(SiO4)x+y(◻T)y(OH)2–xOy◻x–y. The formation of important hydroxyl vacancies in the hexagonal channel of the HAp structure leads to the stabilization of silicocarnotite (that can be considered as a polymorph of the highly Si-substituted HAp phase). The Ca10(PO4)4.9(2)(SiO4)1.1(2)(OH)1.0(1)O0.66(7) composition appears then to be the end-member of the hexagonal Si-HAp solid solution. Silicocarnotite is formed above this silicate insertion level.

Decomposition of TiH2 studied in situ by synchrotron X-ray and neutron diffraction

Decomposition during constant heating of as-received and pre-oxidized titanium hydride (TiH2) powder under flowing and stationary Ar was studied in situ by synchrotron X-ray and neutron diffraction. Diffraction data were compared to corresponding thermoanalysis traces in order to relate peaks of H2 release with individual phase transformations. We found that every peak of H2 release is correlated with regimes of lattice parameter contraction. Core–shell models to describe the decomposition processes measured were found, and further verified by electron microscopy. The models show that a shell of the hexagonal close-packed hydrogen solid solution (α) around each particle core controls its dehydrogenation for as-received TiH2, while a TiO2 rutile shell controls the outgassing from the pre-oxidized powder.

New data on the composition of metacinnabar and Hg-sphalerite with an isomorphous Cd admixture

The data on the composition of metacinnabar and Hg-sphalerite with an isomorphous Cd admixture from some mercury and complex ore objects are summarized. There are two varieties of metacinnabar: (1) cadmium-rich (9.25–15.80 wt.%), with the minimum quantity of Zn admixture (0.67–3.94 wt.%), which has the idealized formula (Hg,Cd,Zn)S (Ulandu) and (2) with increased amounts of Zn (2.21–10.83 wt.%) and Cd (6.00–14.10 wt.%), having the formula (Hg,Zn,Cd)S (Arzak, Kadyrel’, Murzinskoe, Ravnou-1, Ravnou-2). The maximum content of isomorphous Cd (15.80 wt.%) was determined in the metacinnabar from the Ulandu ore occurrence. The Hg-sphalerites are compositionally divided into two groups: (1) with an increased Cd concentration (up to 7.96 wt.%) and (2) mainly with a low content of Cd admixture (0.0 n–1.63 wt.%). The sphalerites of the first group are typical of mineral assemblages including Cd-Zn-enriched metacinnabar (Arzak, Kadyrel’, Murzinskoe, Sarasa). The sphalerite of the Sarasa deposit is included into this group arbitrarily, because it contains more cadmium than the sphalerites of the second group, which are constituents of parageneses only with Zn-metacinnabar or lacking it (Nikitovka, Khaidarkan, Dzhizhikrut, Bayan-Khan, Aktash). There are some Hg-bearing varieties of sphalerite with the idealized formulas (Zn,Hg,Fe)S, (Zn,Hg,Cd)S, (Zn,Cd,Hg,Fe)S, (Zn,Fe,Cd,Hg)S, (Zn,Hg,Cd,Fe)S, (Zn,Fe,Hg,Cd)S, and (Zn,Hg,Cu)S, which transforms into (Zn,Cu,Hg)S. The maximum Cd admixture (7.96 wt.%) was established in Hg-sphalerite from the Kadyrel’ ore occurrence. It is the highest content observed in natural Hg-bearing β-ZnS. The studied metacinnabar and sphalerite varieties are the only cubic phases of the natural system Zn–Hg–Cd–S, which is sometimes expanded because of minor admixtures of other metals. These varieties have a structure identical to the cubic phases of the synthetic systems Me–S and Me–Me–S, where Me = Zn, Cd, and Hg. None of Hg-bearing hexagonal solid solutions were found in the natural system Zn–Hg–Cd–S. The continuity of the natural isomorphous series ZnS cub–HgS cub has not been confirmed by finding of natural intermediate solid solutions at the series fragment between (Zn 0.752Hg 0.248)S and (Hg 0.539Zn 0.461)S. The metacinnabar varieties enriched in both Zn and Cd show no correlation between these elements. It is assumed that the host rocks with an increased content of cadmium compounds were the source of Cd for the formation of specific varieties β-HgS and β-ZnS.

Synthesis and Electrical Conductivity of La1−xSrxAl0.9Mg0.1O3−δ (x = 0.1–0.4) Perovskite Solid Solution

Perovskite solid solution powders of (La1−xSrx)(Al0.9Mg0.1)O3−δ (x = 0.1−0.4) were prepared by a coprecipitation method using corresponding aqueous solutions and ammonium carbonate solution. The X-ray diffraction patterns for the compositions of x = 0.1−0.4 were identified as those of hexagonal LaAlO3 solid solutions. The bulk conductivity of (La0.6Sr0.4) (Al0.9Mg0.1)O3−δ by AC method at 1 V was independent of the oxygen partial pressure and 2.33 ×10−3 Scm−1 at 800°C, suggesting the oxide ion conduction. The activation energy of bulk conductivity was 111 kJmol−1 at 300–500 °C. The grain boundary conductivity increased from 2.02×10−6 Scm−1 at Po2 = 10−15 Pa to 1.11×10−5 Scm−1 at Po2 = 2.1×104 Pa at 800 °C. Hole conduction contributed to the increased conductivity. DC conductivity of (La0.6Sr0.4)(Al0.9Mg0.1)O3−δ depended on the applied voltage and temperature. In N2 atmosphere, hole conductivity overlapped oxide ion conductivity at a high applied voltage (E > 1 V) because of the chemical reaction between positively charged oxide vacancy and N2 gas (Vo·· + N2 → 2No′ + 4h·).

Synthesis of (Gd0.95Eu0.05)(OH)3 Nanomaterials and Their Transformation into Single Crystalline (Gd0.95Eu0.05)2O3 with Enhanced Photoluminescence Properties

In this work, hexagonal solid solutions of (Gd0.95Eu0.05)(OH)3 with two distinctive morphologies of nanorods and nanotubes were successfully synthesized via hydrothermal treatment of mixed nitrate solutions in the presence of ammonium hydroxide. The hydroxide samples exhibited characteristic Eu3+ photoluminescence through the energy transfer from Gd3+ to Eu3+ and the self-excitation of Eu3+. The hydroxide precursors transformed into cubic (Gd0.95Eu0.05)2O3 at ∼500 °C via an intermediate monoclinic (Gd0.95Eu0.05)OOH phase, and the Eu3+ coordination accordingly experienced symmetry changes from D3h to C2v, and then to C2/S6. The cubic (Gd0.95Eu0.05)2O3 well retained the original morphologies of their polycrystalline precursors and exhibited a single-crystalline character at 1000 °C . Greatly enhanced photoluminescence (∼5000 times that of the hydroxides) was observed for the phase conversion.

Rare‐Earth‐Substituted Sr1−xLnxFe12O19 Hexagonal Ferrites

A systematic study on the phase formation and magnetic properties of M‐type hexagonal ferrite solid solutions Sr1−xLnxFe12O19 with rare‐earth ions Ln=Pr, Nd, Sm, Eu, and Gd was performed. All ferrite samples were prepared by the mixed oxide route and characterized with a combination of powder XRD, microscopy, electron‐probe microanalysis, and thermal analysis. For Ln=Pr, Nd, and Sm, the formation of M‐type ferrite solid solutions with limited solubility of rare earths was observed. The lattice parameters of Sr1−xLnxFe12O19 exhibit a linear variation with x within the range of ferrite solid solution, i.e., c0 decreases with x. For Eu‐ and Gd‐containing samples substituted X‐type ferrites are observed. The solubility limits of the rare‐earth ions within the M‐type ferrite lattice range from x=0.46 for Pr to about x=0.17 for Sm. Eu and Gd can be substituted to lesser amounts in the X‐type ferrites. The saturation magnetization at T=5 K increases with increasing rare‐earth concentration for Pr, Nd, and Sm. Mössbauer spectrometry reveals signals originating from Fe3+ on five different crystallographic positions of the M‐type structure as well as ferrous ions on Fe 2a sites. The spectra of the hexagonal ferrites with different rare‐earth ions (La, Pr, Nd, Sm) are very similar and show systematic variations of the hyperfine fields with rare‐earth concentrations.

ChemInform Abstract: Formation of the Hexagonal Ca1-xSrxAl12O19 Solid Solution.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The Ni-Re-Ti (Nickel-Rhenium-Titanium) System

The Ni-Re system [Massalski 2] is a simple peritectic system (Fig. 1). At the Ni side of the Ni-Re system face centered cubic (fcc) solid solution c forms through a peritectic reaction L + e1M c at 17.4 at.% Re, the peritectic reaction temperature being 1620 C. e1 is the close packed hexagonal (cph) terminal solid solution of Re. The Ni-Ti system [Massalski 2] has three intermediate phases Ni3Ti(h), NiTi(u) and NiTi2(p) of which the h and u phases melt congruently at 1380 and 1310 C, respectively (Fig. 2). The p phase forms through a peritectic reaction L + uM p at 984 C. Three eutectic reactions L M c + h, L M h + u and L M a + p, where a is the body centered cubic (bcc) terminal solid solution of bTi, occur at 1304, 1118, and 942 C, respectively. Two eutectoid reactions a M p + e2 where e2 is the cph terminal solid solution of aTi, and uM h + p occur at 765 and 630 C, respectively. The Re-Ti system [Massalski 2] has only one intermediate phase Re24Ti5(v), which forms through a peritectic reaction L + e1M v at 2750 C. A peritectic reaction L + vM a occurs at 2025 C. The a phase transforms to e2 phase at temperatures £882 C (Fig. 3).

The Cr-Ni-Hf (Chromium-Nickel-Hafnium) System

The Cr-Ni-Hf system was reviewed by [2001Gup]. For development of high temperature resistant brazing alloys, the Cr-Ni-Hf system was studied at the Ni-corner. The results are reported here. In order to discuss the results it is necessary to recapitulate the binary systems. The Cr-Hf system [Massalski2] (Fig. 1) has only one intermediate phase Cr2Hf which exists in two polymorphic forms in high temperature Cr2Hf (Y) phase and a low temperature Cr2Hf (Y1) phase. The Y phase melts congruently at 1825 C and the polymorphic transformation temperature for the Cr2Hf phase is 1335 C. Two eutectics, LM a + Y and LM Y + a1, occur at 1665 and 1500 C, respectively. The a and a1 phases are the two body centered cubic (bcc) terminal solid solutions (Cr) and (bHf), respectively. A eutectoid reaction a1MY + x occurs at 1370 C; x is the close packed hexagonal (cph) terminal solid solution (aHf). The Cr-Ni system [1991Nas] (Fig. 2) is a simple eutectic system. The eutectic reaction LM c + a occurs at 1345 C, where c is the face centered cubic (fcc) terminal solid solution (Ni). The c phase extends to 50 at.% Cr and the bcc a phase extends to 32 at.% Ni. An ordered CrNi2 phase forms from the c phase at T < 600 C. The Hf-Ni system [1991Nas] (Fig. 3) has nine intermediate phases: HfNi5 (e), Hf2Ni7 (p), high temperature HfNi3 (k1) and a low temperature HfNi3 (k), Hf8Ni21 (h), Hf3Ni7 (w), Hf7Ni10 (b), Hf9Ni11 (m), HfNi (/1) phase at high temperature and HfNi (/) at low temperature, and Hf2Ni (n). The polymorphic transformation temperatures for the HfNi3 and HfNi phases are 1200 and 1175 C, respectively. The p and /1 phases melt congruently at 1460 and 1530 C, respectively. All other phases form through peritectic reactions: L + pM e at 1240 C, L + pM k1 at 1340 C, L + k1M h at 1300 C, L + hM w at 1350 C, L + /1 M m at 1340 C, L + m M b at 1290 C, and L + /1 M n at 1200 C. Three eutectic reactions LM c + e, LMw + b, and LM n + x occur at 1190, 1190, and 1150 C, respectively. The h and w phases exist at high temperature and transforms through eutectoid reactions hM k + w at 1177 C and wM k + b at 1020 C. The binary phases and their structure data are given in the review by [2001Gup]. No ternary phase exists in the Cr-Hf-Ni system. The Cr-Hf-Ni system has been reinvestigated at the Ni-Corner of the Cr-Hf-Ni system by [1999Kho]. Twenty two alloys were prepared using 99.98 mass% Cr, 99.9 mass% Hf, and 99.95 mass% Ni. The alloys were arc melted

H ordering in hcp M–H systems (M=Sc, Y; Ti, Zr)

The H-sublattice ordering and the effect of local atomic relaxations due to H interstitial atoms on the structural stability of hexagonal hydrogen-M solid solutions (M = Sc, Ti, Y, Zr) is studied by means of the density functional theory. A first-principle based model is presented which, by considering the relaxation of the host metal cell, yields for the first time a suitable explanation for the observed chain-like short range ordering through a coherent stress field along the chain as well as its limitation to only six hcp metals, namely Sc, Y, Ho, Er, Tm, and Lu, and the absence of a mono-hydride phase in the same elements.

Electronic structure of tungsten carbonitrides WC1−x N x

A full potential FLAPW-GGA method is used for the first time to study the electronic structure of hexagonal solid solutions of tungsten carbonitrides WC1−x N x (0 ≤ x ≤ 0.5) and to calculate their equilibrium structural parameters, density, cohesion energy, and coefficients of low-temperature heat capacity and Pauli paramagnetic susceptibility. They are discussed in comparison with similar values for initial binary phases: WC and WN and also hypothetical solid solutions WB0.5C0.5 and WB0.5N0.5.

Polymorphism of BaTiO3 Acceptor Doped with Mn3+, Fe3+, and Ti3+

The effect of Mn doping on the cubic to hexagonal phase transition temperature in BaTiO3 has been determined by quenching samples with different Mn contents from a range of temperatures. Under conditions of equilibrating samples in air over the range 1000°–1400°C, cubic solid solutions BaTi1−xMnxO3−δ form over the range 0≤x≤0.015(5), whereas hexagonal solid solutions form for x≥0.02, depending on the temperature. The results are compared with those on doping BaTiO3 with Fe3+ and observations made concerning acceptor doping with Ti3+.