Solid-state reactions in the system Li<Subscript>2</Subscript>CO<Subscript>3</Subscript>-Na<Subscript>2</Subscript>CO<Subscript>3</Subscript>-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript>

The formation mechanisms of Li _x Na_{1 ?x} Ta _y Nb_{1 ? y} O₃ perovskite solid solutions in the Li₂CO₃-Na₂CO₃-Nb₂O₅-Ta₂O₅ system have been studied by x-ray diffraction, differential thermal analysis, thermogravimetry, IR spectroscopy, and mass spectrometry at temperatures from 300 to 1100°C. The results indicate that the synthesis of Li _x Na_{1 ? x} Ta _y Nb_{1 ? y} O₃ solid solutions involves a complex sequence of consecutive and parallel solid-state reactions. An optimized synthesis procedure for Li _x Na_{1 ? x} Ta _y Nb_{1 ? y} O₃ solid solutions is proposed.     

Phase equilibria and crystal structures of solid solutions in the Sr-Fe-Ni-O system at 1100°C in air

The phase equilibria in the Sr-Fe-Ni-O system at 1100°C in air have been studied by x-ray diffraction, and the corresponding phase diagram at constant temperature and pressure has been constructed. The system has been shown to contain two solid-solution series at 1100°C in air: SrFe_{1 ? x} Ni _x O_{3 ? δ} (0 < x ≤ 0.075, sp. gr. Cmmm) and Sr₃(Fe_{1 ? y} Ni _y )₂O_{7 ? δ} (0 < y ≤ 0.15, sp. gr. I4/mmm). Neither Sr₄(Fe_{1 ? z} Ni _z )₆O₁₃ nor Sr(Fe_{1 ? z} Ni _z )₁₂O₁₉ solid solutions have been identified. The lattice constants and structural parameters of single-phase samples have been refined by the full profile Rietveld analysis method.     

Mechanism of structure formation in samarium and holmium titanates prepared from mechanically activated oxides

We have studied the formation mechanism and phase transitions of samarium and holmium titanates prepared from mechanically activated oxide mixtures with the overall compositions Sm₂(Ho₂)Ti₂O₇ and Sm₂TiO₅. Mechanical activation of oxide mixtures leads to the formation of amorphous solid phases which crystallize in a distorted pyrochlore-like structure and contain OH groups on the oxygen site and structural vacancies up to 1000°C. In the range 800–1000°C, Sm_2?x Ti_1?y O_5?δ (OH) _n (x < 0.02; y < 0.08; δ, n < 0.19) converts to a distorted orthorhombic phase as a result of the relaxation of internal stress and removal of OH groups. Above 1000°C, the phases studied have the compositions Sm₂(Ho₂)Ti₂O₇ and Sm₂TiO₅ and ordered pyrochlore-like and orthorhombic structures, respectively. The lattice parameters of the titanates have been measured in the range 800–1350°C. The internal stress produced by mechanical activation in the phases studied here fully relaxes by ～1300°C.     

Phase equilibria and crystal structures of phases in the La-Fe-Ni-O system at 1370 K in air

The phase equilibria in the La-Fe-Ni-O system have been studied at 1370 K in air, and the La-Fe-Ni-O phase diagram at constant temperature and pressure has been constructed. Based on x-ray diffraction results for samples prepared by standard solid-state reactions and via citrate and nitrate routes, the following solid solutions have been shown to exist at 1370 K in air: LaFe_{1 ? x} Ni _x O_{3 ? δ} (0 < x ≤ 0.4, sp. gr. Pbnm; 0.6 ≤ x ≤ 0.8, sp. gr. R-3 c), La₄(Ni_{1 ? y} Fe _y )₃O_{10 ? δ} (0 < y ≤ 0.3), La₃(Ni_{1 ? z} Fe _z )₂O_{7 ? δ} (0 < z ≤ 0.05), La₂Ni_{1 ? v} Fe _v O_{4 + δ} (0 < v ≤ 0.05), Ni_kFe_{3 ? k} O₄ (0.81 ≤ k ≤ 1.05), Ni_{1 ? m} Fe _m O (0 < m ≤ 0.05), and Fe_{2 ? p} Ni _p O₃ (0 < p ≤ 0.04). The lattice constants and structural parameters of single-phase samples have been refined by the Rietveld profile analysis method.     

Rare-earth-doped PbTiO<Subscript>3</Subscript>-PbZrO<Subscript>3</Subscript> solid solutions

(Pb_{1 ? x} Ln _x )(Zr_0.53Ti_0.47)O₃ and (Pb_{1 ? x} Ln _x )(Zr_0.65Ti_0.35)O₃ (x = 0.02, 0.06; Ln = La, Pr, Gd, Yb) solid solutions have been prepared by modified solid-state synthesis using organic-ligand precursors. The solid solutions have been characterized by thermal analysis, IR spectroscopy, x-ray powder diffraction, and atomic force microscopy. All of them have a rhombohedrally distorted perovskite structure (sp. gr. R3c).     

Synthesis and photocatalytic activity of anatase-based aerogels

V_xTi_1–xO₂ (x = 5 and 10 mol %) solid solutions have been synthesized through supercritical drying in isopropanol at t = 250°C and p = 10 MPa. Their physicochemical properties and photocatalytic performance have been compared to those of an earlier synthesized Zn_xTi_1–xO₂ aerogel containing 10 mol % Zn [1]. It has been shown that increasing the vanadium content of V_xTi_1–xO₂ from 5 to 10 mol % leads to a decrease in hydrogen evolution rate in methanol/water splitting reaction under UV irradiation from 190 to 32 µL/(min g_catal), whereas in the case of the anatase-based aerogel solid solution containing 10 mol % Zn an opposite picture is observed: the hydrogen evolution rate in methanol/water splitting reaction under UV irradiation increases sharply to 700 µL/(min g_catal).     

Phase equilibria and crystal structures of solid solutions in the system LaCoO<Subscript>3−δ</Subscript>-SrCoO<Subscript>2.5±δ</Subscript>-SrFeO<Subscript>3−δ</Subscript>-LaFeO<Subscript>3−δ</Subscript>

The composition region and structure of La_1?x Sr _x Co_1?y Fe _y O_3?δ solid solutions are determined by x-ray powder diffraction using the Rietveld profile analysis method. The solid solutions based on lanthanum cobaltite, LaCoO_3?δ, have a rhombohedrally distorted perovskite-like structure (sp. gr. R \(\bar 3\) c), and those based on lanthanum ferrite, LaFeO_3?δ, have an orthorhombically distorted structure (sp. gr. Pbnm). The rhombohedral distortion decreases with increasing strontium content, and the solid solutions with x ≥ 0.5 have an ideal cubic structure (sp. gr. Pm3m). The composition dependences of lattice parameters for the La_1?x Sr _x Co_1?y Fe _y O_3?δ solid solutions are presented, and the 1100°C isotherm of the LaCoO_3?δ-SrCoO_2.5±δ-SrFeO_3?δ-LaFeO_3?δ system in air is constructed.     

Synthesis of New Crystalline Pu(V) Compounds from Solutions: II. Double Pu(V) Oxalates with Co(NH<Subscript>3</Subscript>)<Subscript>6</Subscript><Superscript>3+</Superscript> Ions in the Outer Sphere

Crystalline compounds of the general composition Co(NH³)⁶PuO₂(C₂O₄)²·nH₂O (n = 2, 3, 5) were isolated from freshly prepared neutral oxalate solutions of Pu(V) by addition of Co(NH₃)₆³⁺ ions. These compounds are fairly stable in storage in air and poorly soluble in water. Previously unknown double Np(V) oxalates Co(NH₃)₆NpO₂(C₂O₄)·nH₂O (n = 2, 5) were also synthesized and studied. All the compounds of Pu(V) and Np(V) of the same composition are mutually isostructural. The behavior of these compounds at heating was studied, and their IR spectra were measured. The optical spectra of new Np(V) compounds were measured.     

Growth and properties of LiCu<Subscript>2</Subscript>O<Subscript>2</Subscript>-NaCu<Subscript>2</Subscript>O<Subscript>2</Subscript> crystals

Platelike Li_{1 ? x} Na _x Cu₂O₂ single crystals up to 2 × 10 × 10 mm in dimensions have been grown by slowly cooling (1 ? x)Li₂CO₃·xNa₂O₂·4CuO melts in alundum crucibles in air. Li_{1 ? x} Na _x Cu₂O₂ solid solutions in the LiCu₂O₂-NaCu₂O₂ system have been shown to exist in the composition range 0.78 < x < 1. The temperature stability ranges of NaCu₂O₂ and LiCu₂O₂ are 780–930 and 890–1050°C, respectively. The Mössbauer spectra and electrical conductivity of the crystals have been measured.     

Structural and dielectric properties of PbMg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript>-PbZrO<Subscript>3</Subscript> solid solutions synthesized at high pressures and temperatures

(1 ? x)PbMg_1/3Nb_2/3O₃ · xPbZrO₃ (1 ? x)PMN · xPZ) solid solutions have been synthesized at a pressure of 5 GPa and temperatures from 1300 to 1700 K, and their structural and dielectric properties have been studied. The composition dependences of the average unit-cell parameter and dielectric permittivity for the solid solutions indicate that the PMN-PZ system has a morphotropic phase boundary near x = 0.65. The solid solutions have a cubic structure for x < 0.65, a rhombohedral structure in the range 0.65 < x < 0.9, and an orthorhombic structure (similar to that of PbZrO₃) for x > 0.9. The temperature and frequency dependences of dielectric permittivity suggest that the (1 ? x)PMN · xPZ samples with x < 0.65 consist of two ferroelectric phases: a relaxor with antipolar dipole order and a normal ferroelectric with a diffuse phase transition. The effect of annealing temperature on the ferroelectric state of the samples with x < 0.65 is examined. In the composition range 0.65 < x < 0.9, the samples have normal ferroelectric properties, independent of annealing temperature.     

Strong up-conversion luminescence and electrical properties of SrBi<Subscript>4</Subscript>Ti<Subscript>4</Subscript>O<Subscript>15</Subscript> multifunctional ceramics by Er<Superscript>3+</Superscript> doping

Novel green-emitting piezoelectric ceramics of SrBi_4?x Er _x Ti₄O₁₅ (SBT-xEr) were prepared. Strong up-conversion with bright green (524 and 548 nm) and a relatively weak red (660 nm) emission bands were obtained under 980 nm excitation at room temperature, which is attributed to the intra 4f–4f electronic transition of (²H_11/2, ⁴S_3/2)–⁴I_15/2 and the transition from ⁴F_9/2 to ⁴I_15/2 of Er³⁺ ions, respectively. Simultaneously, Er³⁺ doping promotes the electrical properties. At 0.8 mol%Er, the optimal electric properties with high Curie temperature of T _c?~527?°C, large remanent polarization of 2P _r?~14.92 μC/cm² and piezoelectric constant of d ₃₃?~17 pC/N was achieved. As a multifunctional material, Er³⁺ doped SBT showed a great potential to be used in 3D-display, bio-imaging, solid state laser and optical temperature sensor.     

Influence of isovalent and heterovalent substitution for Bi<Superscript>3+</Superscript> and Fe<Superscript>3+</Superscript> on the properties of Bi<Subscript>2</Subscript>Fe<Subscript>4</Subscript>O<Subscript>9</Subscript>-based solid solutions

Bi_2–хLa_хFe₄O₉ and Bi₂Fe_4–2xTi_xCo_xO₉ ferrites have been prepared by solid-state reactions at a temperature of 1073 K. X-ray diffraction data indicate that, in the Bi_2–хLa_хFe₄O₉ system, the limiting degree of La³⁺ substitution for Bi³⁺ ions in Bi₂Fe₄O₉ does not exceed 0.05 and that the limiting degree of substitution in the Bi₂Fe_4–2xTi_xCo_xO₉ system lies in the range 0.05 < x < 0.1. The specific magnetization and specific magnetic susceptibility of the samples have been measured at temperatures from 5 to 300 K in a magnetic field of 0.86 T. The field dependences of magnetization obtained for the Bi_2–хLa_хFe₄O₉ and Bi₂Fe_4–2xTi_xCo_xO₉ ferrites at temperatures of 300 and 5 K demonstrate that partial isovalent substitution of La³⁺ for Bi³⁺ ions in Bi₂Fe₄O₉ and heterovalent substitution of Ti⁴⁺ and Co²⁺ ions for two Fe³⁺ ions leads to partial breakdown of the antiferromagnetic state and nucleation of a ferromagnetic state.     

Stability region of Gd<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3 ± δ</Subscript> solid solutions in air

The solid-solution range of Gd_{2 ? x} Mn _x O_{3 ± δ} has been determined using X-ray diffraction analysis of samples with 0.90 ≤ x ≤ 1.20 (Δx = 0.02) prepared from oxide mixtures by solid-state reactions in air between 900 and 1400°C. The results have been used to construct a partial phase diagram of the Gd-Mn-O system in air. It is shown that gadolinium manganite with the perfect metal stoichiometry, GdMnO_{3 ± δ}, does not exist. The material of this composition in air consists of two phases: a Gd_{2 ? x} Mn _x O_{3 ± δ} solid solution with an orthorhombic perovskite-like structure and the binary oxide Gd₂O₃. The solid solution extends to the composition Gd_0.96Mn_1.04O_{3 ± δ}. Over the entire temperature range studied, gadolinium oxide does not dissolve in Gd_0.96Mn_1.04O_{3 ± δ}. Mn₃O₄ exhibits significant solubility in Gd_{2 ? x} Mn _x O_{3 ± δ}. In particular, Gd_0.86Mn_1.14 O_{3 ± δ} is single-phase by X-ray diffraction in the temperature range 1185–1400°C. Below 1185°C, Gd_{2 ? x} Mn _x O_{3 ± δ} is in equilibrium with another gadolinium manganite, GdMn₂O₅. With decreasing synthesis temperature, the GdMn₂O₅ solubility in Gd_{2 ? x} Mn _x O_{3 ± δ} drops precipitously. At 900°C, the only single-phase sample was Gd_0.96Mn_1.04O_{3 ± δ}.     

Thermal expansion and electrical conductivity of La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>Mn<Subscript>1 − <Emphasis Type="Italic">y</Emphasis></Subscript>Cr<Subscript>y</Subscript>O<Subscript>3</Subscript>

The thermal expansion and electrical conductivity of La_0.7Sr_0.3Mn_{1 ? y} Cr_yO₃ (y = 0, 0.1, 0.3, 0.4) solid solutions have been studied at temperatures from 300 to 1270 K and oxygen partial pressures from 10^?9 to 2.1 × 10⁴ Pa. The solid solutions crystallize in rhombohedral symmetry (sp. gr. R3c). The lattice parameters of La_0.7Sr_0.3Mn_{1 ? y} Cr_yO₃ decrease with increasing chromium content. Doping with chromium reduces the conductivity of lanthanum manganite, without changing the conductivity type. The charge transport in the solid solutions is due to small-polaron hopping. Disproportionation of the 3d transition metals is shown to play a key role in determining the electrical properties of the solid solutions. Partial chromium substitution for manganese reduces the thermal expansion coefficient of the manganite, improving its compatibility with yttria-stabilized zirconia, which is of practical importance.     

Enhancing the microwave dielectric properties of Sr<Subscript>2</Subscript>Ca<Subscript>3</Subscript>Ta<Subscript>4</Subscript>TiO<Subscript>17</Subscript> ceramics by Zr Substitution

The compositions in Sr₂Ca₃Ta₄Ti_1?xZr_xO₁₇ (0?≤?x?≤?0.12) series were designed and fabricated by solid state sintering method. All the compositions formed single phases and crystallized in an orthorhombic crystal structure. Zr substitution led to the enhancing of the microwave dielectric properties by tuning the τ_f value through zero and increased the Q_uf_o value from 12,540 to 14,970 GHz with a slight decrease in ε_r. In the present study, a good combination of ε_r ~?51, Q_uf_o ~?145,43 GHz and τ_f ~ 3 ppm/°C were obtained for Sr₂Ca₃Ta₄Ti_0.90Zr_0.1O₁₇ ceramic sintered at 1575 °C for 4 h.     

Perovskite M<Superscript>I</Superscript>M<Superscript>II</Superscript>O<Subscript>3</Subscript> as a matrix for incorporation of the actinide fraction of HLW

Perovskites of the compositions xLa₂O₃·Al₂O₃ and xLa₂O₃·Fe₂O₃ were prepared by cold pressing and sintering at temperatures of up to 1500°C, and their properties were studied. Perovskites based on lanthanum aluminate are more porous than those based on lanthanum ferrite, whereas the rate of radionuclide leaching from the former compounds is lower than from the latter compounds. The parameter x varied in a relatively wide range does not affect the leaching rate.     

Synthesis,X-ray structure analysis,and Raman spectroscopy of R<Subscript>2</Subscript>TiO<Subscript>5</Subscript>-based (R = Sc,Y) solid solutions

Order–disorder transitions in xR₂O₃ · (1 ? x)TiO₂ (R = Sc, 0.4 ≤ x ≤ 0.5; R = Y, 0.5 ≤ x ≤ 0.6) solid solutions with highly imperfect fluorite-derived structures have been studied using monochromatic synchrotron X-ray diffraction and Raman spectroscopy. The results demonstrate that the synthesis process leads to the formation of a fluorite-like (Fm3m) disordered phase and a nanoscale (~10–100 nm) pyrochlore-like (Fd3m) ordered phase of the same composition, coherent with the disordered phase. We have determined their lattice parameters. The Raman spectra of Sc₂TiO₅ (Y₂TiO₅) contain broad lines in low- and high-frequency regions: at 190, 350, and 775 (134, 188, 365, 404, and 727) cm^?1. These lines are characteristic of a pyrochlore-like phase with a varying degree of order and a disordered fluorite-like phase, respectively. The pyrochlore-like phase Y₂Ti₂O₇ has two strong Raman peaks in the low-frequency region: at 312 and 527 cm^?1. The formation of nanodomains with different degrees of order is caused by the internal stress that arises from the high density of structural defects in the unit cells of the solid solutions.     

Na<Subscript>2</Subscript>MoO<Subscript>4</Subscript>-CaMoO<Subscript>4</Subscript>-Ce<Subscript>2/3</Subscript>MoO<Subscript>4</Subscript> scheelite-like solid solutions

We have studied tetragonal scheelite-like solid solutions in the ternary system Na₂MoO₄-CaMoO₄-Ce_2/3MoO₄: Na _0.7Ca_y Ce_{1.1 ? 2y/3} (MoO₄)₂ (0 ≤ y ≤ 0.6) and Na_0.3 Ca_zCe_{1.23? 2z/3} (MoO₄)₂ (0 ≤ z ≤ 1.4). The solid solutions melt congruently at temperatures from 1100 to 1200°C. Their lattice parameters have been determined. Using reflection spectra, we evaluated the color parameters of all the samples studied.     

Low temperature sintering and microwave dielectric properties of Li<Subscript>6</Subscript>Mg<Subscript>7</Subscript>Ti<Subscript>3</Subscript>O<Subscript>16</Subscript> ceramics with LiF additive for LTCC applications

Li₆Mg₇Ti₃O₁₆ ceramics were prepared by the conventional solid-state method with 1–5 wt% LiF as the sintering aid. Effects of LiF additions on the phase compositions, sintering characteristics, micro-structures and microwave dielectric properties of Li₆Mg₇Ti₃O₁₆ ceramics were investigated. The LiF addition could effectively lower the sintering temperature of Li₆Mg₇Ti₃O₁₆ ceramics from 1550 to 900 °C. For different LiF-doped compositions, the optimum dielectric permittivity (ε _r ) and quality factor (Q·f) values first increased and then decreased with the increase of LiF contents, whereas the temperature coefficient of resonant frequency (τ _f ) fluctuated between ??14.39 and ??8.21 ppm/°C. Typically, Li₆Mg₇Ti₃O₁₆ ceramics with 4 wt% LiF sintered at 900 °C exhibited excellent microwave dielectric properties of ε _r ?=?16.17, Q·f?=?80,921 GHz and τ _f ?=???8.21 ppm/°C, which are promising materials for the low temperature co-fired ceramics applications.     

Electrical conductivity of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-Tm<Subscript>2</Subscript>O<Subscript>3</Subscript>-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> solid solutions

New solid solutions, Bi_2?x?y Tm _x Nb _y O_3+δ, with tetragonal and cubic structures have been synthesized in the Bi₂O₃-Tm₂O₃-Nb₂O₅ system, and their electrical conductivity has been measured at temperatures from 670 to 1020 K. The 1020-K conductivity of the tetragonal solid solution Bi_1.8Tm_0.15Nb_0.05O_3+δ is comparable to that of Bi_1.75Tm_0.25O₃, the best conductor in the Bi₂O₃-Tm₂O₃ system.