Solid Solution Limit Research Articles

Microwave dielectric properties of low-loss (Zn1−xCox)3Nb2O8 ceramics for LTCC applications

The phase relation, crystal structure and microwave dielectric properties of (Zn1−xCox)3Nb2O8 ceramics were investigated. The limit of (Zn1−xCox)3Nb2O8 solid solutions was approximately x=0.4. With an increasing x, the corrected dielectric constant decreased and the temperature coefficient of resonant frequency (τf) increased. The τf value is strongly dependent on the tilting of the oxygen octahedral, which can be evaluated by the B-site bond valence. However, a tremendous loss reduction can be achieved by a small amount of Co substitution due to the increase in relative density and packing fraction. The B2O3 and CuO addition can effectively lower the sintering temperature of (Zn0.95Co0.05)3Nb2O8 without seriously deteriorating the dielectric properties. For LTCC applications, the 4wt% B2O3–CuO doped (Zn0.95Co0.05)3Nb2O8 ceramic sintered at 930°C is a good choices because of its excellent dielectric properties (ɛr∼20.75, Q×f∼105,000GHz and τf∼−83.7ppm/°C) and the chemical compatibility with silver.

THE SYSTEM Hg-Pd-Se AT 400 C: PHASE RELATIONS INVOLVING TISCHENDORFITE AND OTHER TERNARY PHASES

Abstract Phase relations in the Hg–Pd–Se system were studied by the evacuated silica glass tube technique. For kinetic reasons, experiments were performed in the range 350–400 oC. We present here the 400 oC condensed isothermal section for the Hg–Pd–Se system, based on literature data and on our experiments. Two ternary phases were known previously: Pd 8 Hg 3 Se 9 , which corresponds to tischendorfite, and Pd 2 HgSe 3 . We report here on a third phase, Pd 5 HgSe. Tischendorfite forms stable assemblages with palladseite (Pd 17 Se 15 ), tiemannite (HgSe), potarite (PdHg), and with the phase Pd 2 HgSe 3 . In turn, Pd 2 HgSe 3 forms stable assemblages with PdSe 2 (orthorhombic), palladseite (Pd 17 Se 15 ), tischendorfite (Pd 8 Hg 3 Se 9 ), and tiemannite (HgSe). The phase Pd 5 HgSe, stable near the Pd-rich corner of the system, forms stable assemblages with metallic Pd, PdHg (potarite), palladseite (Pd 17 Se 15 ), and other Pd-rich binary palladium selenides. Palladseite forms limited solid-solution and dissolves up to 4.15 at.% Hg at 350 oC. This solid solution forms stable assemblages with Pd 8 Hg 3 Se 9 , PdSe 2 , and HgPd (potarite). There are no joins involving HgSe (tiemannite) and binary Pd selenides.

Yb-doped LiGd1−xLux(WO4)2 single crystal fibers grown from the melt and optical characterization

As a function of lutetium concentration, Yb(1at%)-doped LiGd1−xLux(WO4)2 phases have been synthesized by solid state reaction. For x≤0.025, a limited solid solution corresponding to the substitution of Gd3+ by Lu3+ in LiGd(WO4)2 compound was observed. In another hand, for x≥0.8 a limited solid solution corresponding to the substitution of Lu3+ by Gd3+ in LiLu(WO4)2 was obtained. Different single crystalline fibers belonging to the Yb (1at%)-doped LiGd1−xLux(WO4)2 system with diameter average 600µm and length up to 30mm have been grown by micro-pulling down method. In the stationary stable growth regime, the crystallization interface was flat and meniscus length reaches 120µm±20. An overheating of the melt causes a strong Li2O loss and composition change in the equilibrium diagram allowing growth instabilities and crystal disconnection from the molten zone. The optical characterizations have been performed. Decay time has been recorded for the 1at% Yb3+ doped fibers.

Trajectory and kinetics of relaxation processes during the crystallization of inorganic alloys

This paper discusses some problems of physicochemical analysis and examines the possibility of gaining insight into the mechanisms underlying the crystallization behavior of inorganic alloys. As a model, we use a eutectic T-x system with two phase-forming structural components and limited solid solutions based on them. We demonstrate that the supramolecular theory of eutectics and current views of solid-state determined can be helpful in predicting the forming metastable structural states.

Analysis of the homogeneity ranges of pollucite-based (analcime-pollucite) solid solutions

The empirical compositions of pollucite (analcime-pollucite) from various occurrences are analyzed using the AO-BO0.5-AlO1.5-SiO2, “AAl2O4”-“BAlO2”-SiO2-H2O, and BO0.5-AlO1.5-SiO2-H2O (A = alkaline-earth element, B = alkali element) composition tetrahedra. Three-dimensional geometric analysis in conjunction with analysis of density and optical properties indicates the presence of several cesium-containing solid solutions differing in structural framework. A key factor in the formation of the structural framework of the Cs-containing zeolite is water content. The limited solid solution Cs2Al2Si4O12 · nH2O contains a negligible amount of water. Most of the empirical compositions of pollucite (analcime-pollucite) lie within the homogeneity regions of solid solutions based on B2Al2Si5O14 · nH2O. One of the samples considered here has a chemical composition analogous to the empirical composition of montesommaite in which Na and Cs substitute for the major alkali element K.

Solid-State (29)Si NMR and neutron-diffraction studies of Sr(0.7)K(0.3)SiO(2.85) oxide ion conductors.

K/Na-doped SrSiO3-based oxide ion conductors were recently reported as promising candidates for low-temperature solid-oxide fuel cells. Sr0.7K0.3SiO2.85, close to the solid-solution limit of Sr1-xKxSiO3-0.5x, was characterized by solid-state (29)Si NMR spectroscopy and neutron powder diffraction (NPD). Differing with the average structure containing the vacancies stabilized within the isolated Si3O9 tetrahedral rings derived from the NPD study, the (29)Si NMR data provides new insight into the local defect structure in Sr0.7K0.3SiO2.85. The Q(1)-linked tetrahedral Si signal in the (29)Si NMR data suggests that the Si3O9 tetrahedral rings in the K-doped SrSiO3 materials were broken, forming Si3O8 chains. The Si3O8 chains can be stabilized by either bonding with the oxygen atoms of the absorbed lattice water molecules, leading to the Q(1)-linked tetrahedral Si, or sharing oxygen atoms with neighboring Si3O9 units, which is consistent with the Q(3)-linked tetrahedral Si signal detected in the (29)Si NMR spectra.

The revised phase diagram of the Ca3(PO4)2–YPO4 system. The temperature and concentration range of solid-solution phase fields

A revised version of the Ca3(PO4)2–YPO4 phase diagram has been proposed on the basis of results obtained by thermal analysis (DTA/DSC/TG) and X-ray diffraction methods. A limited solid solution with the structure of β-Ca3(PO4)2 exists in the system. At 1,100 °C the maximal concentration of YPO4 in the solid solution is ~15 mass%. The solid-solution phase field exists in the temperature range upto ~1,380 °C. Two high-temperature solid solutions with the structure of α′ and α-Ca3(PO4)2 form in system as well, however only the α phase can be obtained by quenching from high temperatures. The Ca3Y(PO4)3 compound with the structure of eulytite forms in the Ca3(PO4)2–YPO4 system at temperatures exceeding 1,255 °C and does not show any polymorphic transition.

THE Ag-Pd-Se SYSTEM: PHASE RELATIONS INVOLVING MINERALS AND POTENTIAL NEW MINERALS

The phase equilibria in the system Ag–Pd–Se were studied by the evacuated-silica glass tube method at 350, 430, and 530 °C. In the system we synthesized four ternary phases: Ag2Pd3Se4 (chrisstanleyite) and the new phases AgPd3Se, (Ag,Pd)22Se6, and Ag6Pd74Se20. The AgPd3Se phase forms a Ag1− x Pd3+ x Se ( x = 0–0.15) solid-solution series. The (Ag,Pd)22Se6 phase forms a (Ag11± x Pd11± x )22Se6 (0.2 ≥ x ≥ 3.9) solid-solution series, the solubility of Ag decreasing with increasing temperature. Palladseite (Pd17Se15) forms a limited solid solution and dissolves up to 7 wt.% Ag, and the phase Pd9Se2 dissolves up to 3 wt.% Ag. The Ag2Pd3Se4 phase, an analogue of the mineral chrisstanleyite, forms stable associations with naumannite (Ag2Se) and veerbekite (PdSe2); it also coexists with palladseite (dissolving 7 wt.% Ag). The phase is stable up to 430 oC. Phase relations determined the mineral assemblages that can be expected to occur in nature. Ternary AgPd3Se and (Ag,Pd)22Se6 phases and the binary PdSe, Pd7Se4, and Pd34Se11 phases can be expected in associations with the mineral palladseite, among other selenides. Finding these phases in nature is highly probable in telethermal selenide veins and unconformity-related uranium deposits, at conditions of high Se/S fugacity ratio, an oxidizing environment, and Se-rich fluids, forming at low temperatures. The Ag6Pd74Se20 phase forms stable associations with AgPd3Se and Pd7Se2. It also coexists with Pd4Se and Pd9Se2. The Ag6Pd74Se20 phase is stable above 430 oC. Under natural conditions the Ag6Pd74Se20 and Pd9Se2 phases can be expected to occur in less traditional environments than are usual for selenides, forming at higher temperatures (above 430 oC).

The phase equilibria and thermal stability of the long-period stacking ordered phase in the Mg–Cu–Y system

Phase equilibria in the Mg-rich Mg–Cu–Y system at 300, 400 and 450°C have been experimentally investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), electron probe micro-analyzer (EPMA) and transmission electron microscope (TEM). The results show that a long-period stacking ordered (LPSO) phase 14H is stable in the Mg–Cu–Y system, which is the only one ternary intermetallic compound that gets a thermodynamic equilibrium with the a-Mg phase. The equilibrium 14H phase has a very limited solid solution range, and can be nearly regarded as a ternary stoichiometric compound with a formulae as Mg91Cu4Y5. The thermal stability of the 14H phase in the Mg–Cu–Y system has been well studied, which shows that the 14H phase disappears varying from 442°C to 490°C depending on the alloy composition. The isothermal sections of the Mg-rich Mg–Cu–Y system at 300, 400 and 450°C have been finally established, and moreover, a quasi-peritectic reaction L+α-Mg↔14H+Mg2Cu has been determined occurring at 442°C with an estimated liquid composition of Mg77Cu18Y5.

Low variation in relative permittivity over the temperature range 25–450°C for ceramics in the system (1−x)[Ba0.8Ca0.2TiO3]–x[Bi(Zn0.5Ti0.5)O3

Abstract The dielectric and ferroelectric properties of the ceramic system, (1 − x)Ba0.8Ca0.2TiO3–xBi(Zn0.5Ti0.5)O3, were investigated for compositions 0 ≤ x ≤ 0.4. X-ray powder diffraction patterns indicated tetragonal symmetry at x ≤ 0.05, switching to pseudocubic at x ≥ 0.1, with a single-phase solid solution limit at 0.2

Electrodeposition of Al-W Alloys in the Lewis Acidic Aluminum Chloride−1-Ethyl-3-Methylimidazolium Chloride Ionic Liquid

The electrodeposition of non-equilibrium Al-W alloys was investigated in the Lewis acidic 66.7‐33.3 percent mole fraction aluminum chloride–1-ethyl-3-methylimidazolium chloride (AlCl3–[EtMeIm]Cl) room-temperature ionic liquid (IL). The W(III) compound, K3[W2Cl9], served as the reservoir for W. Both controlled potential and controlled current techniques were employed. Depending on the electrodeposition conditions, it was possible to prepare Al-W alloys with a W content approaching 96 percent atomic fraction (a/o). However, as the W content of these alloys increased above 30 a/o, the deposits became powdery and friable and were difficult to characterize. XRD analysis of deposits containing ∼16 a/o W revealed a broad reflection consistent with the amorphous phase that typically appears at alloy concentrations that exceed the limit of the supersaturated solid solution. This phase is not readily apparent in X-ray diffraction patterns until the W content reaches about 9 a/o. As expected, the lattice parameter for the fcc Al phase decreased as the W content of the alloy increased, reaching a maximum contraction of about 0.2%, consistent with a W content of about 5 a/o. This suggests that the amorphous phase may be present in deposits containing a little as 5 a/o W. Alloys containing ∼3 a/o W were dense and compact and displayed a chloride pitting potential of +0.3 V versus unalloyed Al. Heat treatment was explored as a method to address the powdery morphology of those deposits with a high W content, but XRD analysis indicated that this approach leads to the precipitation of at least one new phase (Al5W) and a decrease in the chloride pitting potential.

Clarification of possible ordered distributions of trivalent cations in layered double hydroxides and an explanation for the observed variation in the lower solid-solution limit

The sequence of hexagonal ordered distributions of trivalent cations that are possible in the octahedral layer of layered double hydroxides is clarified, including the link between the composition and the supercell a parameter. A plausible explanation is provided for the observed variation in the lower solid-solution limit.

Application of the regular solution model to analyzing the interaction in binary fluoride systems

Binary fluoride systems were considered in the frame of the regular solution model. An interaction parameter based on which the nature of the interaction in the systems can be suggested was calculated for melting diagrams of the eutectic type and also for diagrams with limited solid solutions and solid solutions with a minimum (or a maximum) in the liquidus curve.

Solid solutioning in equiatomic alloys: Limit set by topological instability

• A series of fcc structured equiatomic solid solutions were designed. • The solid solution limit in multi-component equiatomic alloys was explored. • Topological instability sets the solid solution limit. • Decomposition occurs when the lattice strain reaches a critical value of 0.018. Solid solutioning in equiatomic alloys becomes an interesting and timely topic, considering the current interest at high-entropy alloys (HEAs) in the materials community. In the circumstances where there is no such a differentiation of the solvent and solutes, it is intriguing to explore the solid solution limit in HEAs. In this work, a series of fcc structured equiatomic alloys were specially designed, following the valence electron concentration rule, to study the solid solutioning in the assumed pseudo binary Ni–X (X = Co, Fe, Cr, Cu) systems. The solid solution limit of the multi-component equiatomic alloys was found to set by the topological instability. The decomposition of the single-phase solid solution occurred when the lattice distortion reached a critical strain of 0.018.

CRYSTAL STRUCTURE DETERMINATION OF A UNIQUE Nb-Ti-RICH THORITE FROM MONT SAINT-HILAIRE, QUEBEC, WITH COMMENTS ON ‘THOROGUMMITE’

The crystal chemistry of a unique Nb-Ti-rich thorite from Mont Saint-Hilaire (Quebec) has been examined by a combination of single crystal and powder X-ray diffraction, electron microprobe analyses, and Fourier-transform infrared spectroscopy. The average of 9 compositions gave (Th 0.21 Nb 0.20 Ti 0.18 Ca 0.13 Y 0.10 REE 0.09 Fe 0.03 Zr 0.01 Sr 0.01 Mn 0.01 K 0.01 Na 0 . 01 ) Σ 1.00 [(Si 0.49 □ 0.41 Al 0.08 P 0.01 S 0.01 ) Σ 1.00 (O 2.33 F 0.02 )](OH) 1.70 . This is the first example in the literature of a zircon-group mineral containing elevated concentrations of Nb (0.20 apfu , 13.33 wt.% Nb 2 O 5 ) and Ti (0.19 apfu Ti, 7.41 wt.% TiO 2 ), and evidence for the (SiO 4 ) 4− ↔ (OH) 4 4− “hydrogarnet” substitution. The crystal structure was solved and refined to R = 3.40% and wR 2 = 9.73% for 68 reflections with F o > 4σ( F o ). The studied thorite is slightly metamict, tetragonal, space group I 4 1 / amd , with a 7.058(1) A, c 6.2260(12) A, V 310.15(11) A 3 , and Z = 4. It is isostructural with other zircon-group minerals and has a unit cell which is 4% smaller than that of thorite sensu stricto , a result of the incorporation of high field-strength elements of smaller radii. The structure consists of one eight-coordinated metal site ( A = Th, Zr, U, REE, Y, Nb, Ti, etc. ), one tetrahedral site ( T ), one O site, and one variably-occupied H site. The A site is coordinated by four axial O atoms [ A –O axial = 2.428(5) A] and four equatorial O atoms [ A –O eq = 2.322(6) A], which define a bisdisphenoid with A –O> = 2.374 A. The T site in MSH thorite is only partially occupied by Si (33% vacant) and coordinated by four O with T –O = 1.641(5) A. A partially occupied H site (31%) is located 0.980 A away from the O atom, forming (O 4 H 4 ) 4− groups when the T site is vacant. Removal of the center of symmetry in the structure allows for the possibility of the presence of bimodal T –O and A –O bond lengths, leading to both short Si–O bonds and longer □–OH bonds, as well as the shorter A –O bonds required for Nb and Ti. Accommodation of Nb and Ti into the thorite structure may be facilitated by increased distortion of the A O 8 bisdisphenoid, relaxation and shortening of A –O bonds as a result of the (SiO 4 ) 4− ↔ (OH) 4 4− substitution, and the likely presence of defects (O vacancies) in regions which have undergone slight metamictization, resulting in short-range ordering of Nb, Ti, and Th. Although it is possible that a metastable, limited solid solution exists between thorite and (OH) 4 4− -dominant “thorogummite” with intermediate compositions defined by Th(SiO 4 ) 1 −x (OH) 4 x , reported compositions indicate otherwise and it is suggested that the name “thorogummite” be abandoned.

Effect of BiYbO3 Solid Solution Limit on Electric Properties and Structure of BSPT Piezoceramics

Effect of BiYbO3 Solid Solution Limit on Electric Properties and Structure of BSPT Piezoceramics

Formation of single crystalline tellurium supersaturated silicon pn junctions by ion implantation followed by pulsed laser melting

Pn junctions based on single crystalline tellurium supersaturated silicon were formed by ion implantation followed by pulsed laser melting (PLM). P type silicon wafers were implanted with 245 keV 126Te+ to a dose of 2 × 1015 ions/cm2, after a PLM process (248 nm, laser fluence of 0.30 and 0.35 J/cm2, 1–5 pulses, duration 30 ns), an n+ type single crystalline tellurium supersaturated silicon layer with high carrier density (highest concentration 4.10 × 1019 cm−3, three orders of magnitude larger than the solid solution limit) was formed, it shows high broadband optical absorption from 400 to 2500 nm. Current—voltage measurements were performed on these diodes under dark and one standard sun (AM 1.5), and good rectification characteristics were observed. For present results, the samples with 4–5 pulses PLM are best.

Study of phase relationships in the Sr3(PO4)2–CePO4 system. Phase diagram and thermal characteristics of phases

A diagram representing phase relationships in the Sr3(PO4)2–CePO4 phosphate system has been developed on the basis of results obtained by thermal analysis (DTA/DSC/TGA) and X-ray diffraction (XRD) methods. One intermediate compound with the formula Sr3Ce(PO4)3 occurs in the Sr3(PO4)2–CePO4 system at temperatures exceeding 1045 °C. The compound has a eulytite structure with the following structural parameters: a=b=c=10.1655(8) Å, α=β=γ=90.00°, V=1050.46(6) Å3. It's melting point exceeds 1950 °C. A limited solid solution exists in the system, which possesses the structure of a low-temperature form of Sr3(PO4)2. At 1000 °C the maximal concentration of CePO4 in the solid solution is below 20 mol%. The solid solution phase field narrows with increased temperature. There is a eutectic point in the {Sr3(PO4)2+Sr3Ce(PO4)3} phase field at 1765 °C and 15 mol% of CePO4. The melting temperature of Sr3(PO4)2 is 1882±15 °C.

Structural evolution, sintering behavior and microwave dielectric properties of (1−x)Li2TiO3 + xLiF ceramics

Structural evolution, sintering behavior, and microwave dielectric properties of (1−x)Li2TiO3+xLiF (0.05≤x≤0.70) ceramics have been studied by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Raman spectra, thermal dilatometry and microwave resonant measurement at the frequency of about 7–11GHz. The results show that Li2TiO3 can form limited solid solution with LiF (x≤0.4) and LiF second phase appeared when x30.5. The structure of the solid solution transformed from ordered monoclinic phase (β-Li2TiO3 (ss)) to disordered cubic rock salt (α-Li2TiO3 (ss)) when x30.15. The presence of short range ordering was confirmed for the cubic phase. The sinterability was considerably improved by doping with LiF. Densified ceramics with about 95–98% theoretical density could be obtained for the doped compositions after sintering at 900–1150°C/2h. An optimized microwave dielectric properties with εr of ~23.6, Q×f of ~108,000GHz and τf of ~4.2ppm/°C could be obtained for the x=0.1 composition after sintering at 1100°C/2h.

Synthesis and Impedance Studies of CuTa2−2xO6−5x Perovskites

Polycrystalline samples of CuTa2-2xO6-5x are successfully synthesised by solid state reaction at 975 °C over 24 hours and the solid solution limit is confirmed as 0 1 ≤ x ≤ 0 2. The samples are fully indexed based on cubic structure in the space group, Pmmm, International Centre for Diffraction data (ICDD) number 70-611. The refined lattice parameters for CuTa1.8O5.5 (x = 0 1) and CuTa1.6O5 (x = 0 2) are a = 7 5117 (4) and 7.5070 (16), respectively. The determined grain sizes for both samples are in the range of 0.5-3.0 μm for x = 0 1 and 1.0-4.0 μm for x = 0 2. Besides, the samples show no thermal change in a wide range of temperature studied. Meanwhile, high relative permittivity exhibited by sample x = 0 2 at room temperature is also accompanied with high dielectric loss. The recorded activation energies, Ea are relatively low ~ 0.28-0.33 eV and high conductivity in higher copper content sample. i.e., x=0.2 is probably attributed to the conductive behavior of copper.