New Yellow Ceramic Pigment Based on Codoping Pyrochlore-type Y2Ti2O7 with V5+ and Ca2+

A new yellow pigment with the pyrochlore structure Ca_xY_{2− x} V _x Ti_{2− x} O₇ was prepared as a substitute for the decreasing variety of available yellow ceramic pigments due to the severe regulation of toxic lead and cadmium. The solubility limit of vanadium in this pigment was found to be 1.5 wt% as V₂O₅ or 0.13 as x in the above formula expression. Characterization of vanadium in the vanadium pyrochlore yellow pigment by electron spectroscopy for chemical analysis and electron spin resonance showed that the oxidation state of vanadium was V⁵⁺ and its yellow color mostly originated from V⁵⁺ substituted for Ti⁴⁺. Comparison of color characteristics of Ca_xY_{2− x} V _x Ti_{2− x} O₇ with those of commercial V–SnO₂ and V–ZrO₂ revealed that Ca _x Y_{2− x} V _x Ti₂₋O₇ had better color strength and brightness than the commercial pigments.     

Effect of V2O5 Doping on the Sintering and Dielectric Properties of M-Phase Li1+x−yNb1−x−3yTix+4yO3 Ceramics

The effect of the addition of V₂O₅ on the structure, sintering and dielectric properties of M -phase (Li_{1+ x − y} Nb_{1− x −3 y} Ti _x +4 _y )O₃ ceramics has been investigated. Homogeneous substitution of V⁵⁺ for Nb⁵⁺ was obtained in LiNb_{0.6(1− x )}V_{0.6 x} Ti_0.5O₃ for x ≤ 0.02. The addition of V₂O₅ led to a large reduction in the sintering temperature and samples with x = 0.02 could be fully densified at 900°C. The substitution of vanadia had a relatively minor adverse effect on the microwave dielectric properties of the M -phase system and the x = 0.02 ceramics had [alt epsilon]_r= 66, Q × f = 3800 at 5.6 GHz, and τ_f= 11 ppm/°C. Preliminary investigations suggest that silver metallization does not diffuse into the V₂O₅-doped M -phase ceramics at 900°C, making these materials potential candidates for low-temperature cofired ceramic (LTCC) applications.     

Formation and Microwave Dielectric Properties of the Mg2V2O7 Ceramics

The formation process and microwave dielectric properties of the Mg₂V₂O₇ ceramics were investigated. The MgV₂O₆ phase that was formed at around 450°C interacted with remnant MgO above 590°C to form a homogeneous monoclinic Mg₂V₂O₇ phase. Finally, this monoclinic Mg₂V₂O₇ phase was changed to a triclinic Mg₂V₂O₇ phase for the specimen fired at 800°C. Sintering at 950°C for more than 5 h produced high-density triclinic Mg₂V₂O₇ ceramics. In particular, the Mg₂V₂O₇ ceramics sintered at 950°C for 10 h exhibited the good microwave dielectric properties of ɛ_r=10.5, Q × f =58 275 GHz, and τ_f=−26.9 ppm/°C.     

Phase Relations In The Pseudo-Ternary System La2O3–SrO–Fe2O3

The phase relations in the pseudo-ternary system La₂O₃–SrO–Fe₂O₃ have been investigated in air. Isothermal sections at 1100° and 1300°C are presented based on X-ray diffraction and thermal analysis of annealed samples. Extended solid solubility was observed for the compounds Sr _{n +1− v} La _v Fe _n O_{3 n +1−δ} ( n =1, 2, 3, and ∞) and Sr_{1− x} La _x Fe₁₂O₁₉, while only limited solubility of La in Sr_{4− z} La _z Fe₆O_13±δ was observed. At high Fe₂O₃ content, a liquid with low La₂O₃ content was stable at 1300°C.     

Effect of Li2CO3 Addition on the Sintering Temperature and Microwave Dielectric Properties of Mg2V2O7 Ceramics

Li₂CO₃ was added to Mg₂V₂O₇ ceramics in order to reduce the sintering temperature to below 900°C. At temperatures below 900°C, a liquid phase was formed during sintering, which assisted the densification of the specimens. The addition of Li₂CO₃ changed the crystal structure of Mg₂V₂O₇ ceramics from triclinic to monoclinic. The 6.0 mol% Li₂CO₃-added Mg₂V₂O₇ ceramic was well sintered at 800°C with a high density and good microwave dielectric properties of ɛ _r=8.2, Q × f =70 621 GHz, and τ_f=−35.2 ppm/°C. Silver did not react with the 6.0 mol% Li₂CO₃-added Mg₂V₂O₇ ceramic at 800°C. Therefore, this ceramic is a good candidate material in low-temperature co-fired ceramic multilayer devices.     

Pyrochlore Phase Formation in the System Bi2O3–ZnO–Ta2O5

The subsolidus phase diagram of the system Bi₂O₃–ZnO–Ta₂O₅ in the region of the cubic pyrochlore phase has been determined at 1050°C. This phase forms a solid solution area that includes the ideal composition P, Bi₃Zn₂Ta₃O₁₄; possible solid solution mechanisms are proposed, supported by density measurements of Zn-deficient solid solutions. The general formula of the solid solutions is Bi_{3+ y} Zn_{2− x} Ta_{3− y} O_{14− x − y} , based on the creation of Zn²⁺, O²⁻ vacancies in Zn-deficient compositions and a variable Bi/Ta ratio.     

Pyrochlore Phases in the System ZnO–Bi2O3–Sb2O5: I. Stoichiometries and Phase Equilibria

Two cubic pyrochlore phases exist in the system ZnO–Bi₂O₃–Sb₂O₅. Neither has the supposed "ideal" stoichiometry, Zn₂Bi₃Sb₃O₁₄. One, P ₁, is a solid solution phase, Zn_{2+ x} Bi_{2.96−( x − y )}Sb_{3.04− y} O_14.04+δ where 0< x <0.13(1), 0< y <0.017(2) and a =10.4285(9)−10.451(1) Å. The other, P ₂, is a line phase, Zn₂Bi_3.08Sb_2.92O_13.92 with a =10.462(2) Å. Subsolidus phase relations at 950°C involving phases P ₁ and P ₂ in the ZnO–Bi₂O₃–Sb₂O₅ phase diagram have been determined.     

Fast Li+ Ion Conduction in Li2O-Al2O3-TiO2-SiO2-P2O5 Glass-Ceramics

Fast lithium ion conducting glass-ceramics have been successfully prepared from the pseudobinary system 2[Li_{1+ x} Ti₂Si _x P_{3− x} O₁₂]-AlPO₄. The major phase present in the glass-ceramics was LiTi₂P₃O₁₂ in which Ti⁴⁺ ions and P⁵⁺ ions were partially replaced by Al³⁺ ions and Si⁴⁺ ions, respectively. Increasing x resulted in a considerable enhancement in conductivity, and in a wide composition range extremely high conductivity over 10⁻³ S/cm was obtained at room temperature.     

Subsolidus Phase Relationships in the Ga2O3–Al2O3–TiO2 System

Subsolidus phase relationships in the Ga₂O₃–Al₂O₃–TiO₂ system at 1400°C were studied using X-ray diffraction. Phases present in the pseudoternary system include TiO₂ (rutile), Ga_{2−2 x} Al_{2 x} O₃ ( x ≤0.78 β-gallia structure), Al_{2−2 y} Ga_{2 y} O₃ ( y ≤0.12 corundum structure), Ga_{2−2 x} Al_{2 x} TiO₅ (0≤ x ≤1 pseudobrookite structure), and several β-gallia rutile intergrowths that can be expressed as Ga_{4−4 x} Al_{4 x} Ti _{n −4}O_{2 n −2} ( x ≤0.3, 15≤ n ≤33). This study showed no evidence to confirm that aluminum substitution of gallium stabilizes the n =7 β-gallia–rutile intergrowth as has been mentioned in previous work.     

Defect Structure and Electrical Properties of La1−ySryFe1−xAlxO3−δ

La_{1− y} Sr _y Fe_{1− x} Al _x O_3−δ perovskites were studied as potential materials for solid-oxide fuel cell (SOFC) cathodes. The phase relations in the LaFeO₃–SrFeO_3−δ–LaAlO₃ system were investigated by X-ray powder diffraction analysis. The defect structure of the La_{1− y} Sr _y Fe_{1− x} Al _x O_3−δ perovskites was investigated by Mössbauer spectroscopy and weight-loss analysis. Relations between the nonstoichiometry and the conductivity of the La_{1− y} Sr _y Fe_{1− x} Al _x O_3−δ perovskites were investigated. The incorporation of aluminum ( x ) into LaFe_{1− x} Al_xO₃ was found to have no influence on the defect structure but to decrease the conductivity. The incorporation of strontium ( y ) into La_{1− y} Sr _y Fe_{1− x} Al _x O_3−δ promotes the formation of anion vacancies and Fe⁴⁺ that lead to higher conductivity.     

A- and B Site Cosubstituted Ba6−3xSm8+2xTi18O54Microwave Dielectric Ceramics

Tin (Sn) substitution into the B-site and Nd/Sn cosubstitution into the A- and B-sites were investigated in a Ba _{6−3 x} Sm_{8+2 x} Ti₁₈O₅₄solid solution ( x = 2/3). A small amount of tin substitution for titanium improved the temperature coefficient of resonant frequency (τ_f) but led to a decrease of the relative dielectric constant (ɛ) and the quality factor ( Qf ). The Ba_{6−3 x} Sm_{8+2 x} (Ti_{1− z} Sn_z)₁₈O₅₄-based tungsten-bronze phase became unstable for compositions with a tin content of ≥10 mol%, where BaSm₂O₄and Sm₂(Sn,Ti)₂O₇appeared, and finally, these phases became the major phases. On the other hand, Nd/Sn cosubstitution led to a good combination of high ɛ, high Qf , and near-zero τ_f. Excellent microwave dielectric properties were achieved in Ba_{6−3 x} (Sm_{1− y} Nd _y )_{8+2 x} (Ti_{1− z} Sn _z )₁₈O₅₄ceramics with y = 0.8 and z = 0.05 sintered at 1360°C for 3 h: ɛ= 82, Qf = 10 000 GHz, and calculated τ_f=+17 ppm/°C. The tolerance factor and electronegativity difference exhibited important effects on the microwave dielectric properties, especially the Qf value. A large tolerance factor and high electronegativity difference generally led to a higher Qf value.     

Synthesis of (Mg,Si)Al2O4 Spinel from Aluminum Dross

The spinel (Mg,Si)Al₂O₄ was synthesized from aluminum dross using an induction synthesis method. X-ray diffraction analyses on products formed at different temperatures provided an understanding of the formation mechanism of the spinel. After removal of soluble components, the induction heating of the dross resulted first in the oxidation of some of the AlN component and the subsequent formation of the spinel by the following reaction: x SiO₂+ (1− x )MgO + [1−( x /3)]Al₂O₃+ (2 x /3)AlN = (Mg_{1− x} ,Si _x )Al₂O₄+ ( x /3)N₂( g ).     

Subsolidus Phase Relations in the Ga2O3-In2O3-SnO2 System

Subsolidus phase relationships in the Ga₂O₃–In₂O₃–SnO₂ system were studied by X-ray diffraction over the temperature range 1250–1400°C. At 1250°C, several phases are stable in the ternary system, including Ga₂O₃( ss ), In₂O₃( ss ), SnO₂, Ga_{3− x} In_{5+ x} Sn₂O₁₆, and several intergrowth phases that can be expressed as Ga_{4−4 x} In_{4 x} Sn _{n −4}O_{2 n −2} where n is an integer. An In₂O₃–SnO₂ phase and Ga₄SnO₈ form at 1375°C but are not stable at 1250°C. GaInO₃ did not form over the temperature range 1000–1400°C.     

Modification of MgAl2O4 Microwave Dielectric Ceramics by Zn Substitution

MgAl₂O₄ microwave dielectric ceramics were modified by Zn substitution for Mg, and their dielectric characteristics were evaluated, along with their structures. Dense (Mg_{1− x} Zn _x )Al₂O₄ ceramics were obtained by sintering at 1550°–1650°C in air for 3 h, and the (Mg_{1− x} Zn _x )Al₂O₄ solid solution was determined in the entire composition range. With Zn substitution for Mg, the dielectric constant ɛ of MgAl₂O₄ just varied from 7.90 to 8.56, while the Q × f value had significantly improved up to a maximal value of 106 000 GHz at x =1.0. Moreover, the τ_f of MgAl₂O₄ ceramics had declined from −73 to −63 ppm/°C.     

Quaternary Compounds Prepared in a CaO–Y2O3–SnO2 System

Compounds in a CaO–Y₂O₃–SnO₂ system were prepared by a solid-state reaction at 1673 K. The phase relation in this system was investigated by powder X-ray diffraction. Besides the previously reported ternary compounds, CaSnO₃, Ca₂SnO₄, Y₂Sn₂O₇, and a quaternary compound Ca_0.4Y_1.2Sn_0.4O₃, solid-solution series of Ca_{2− x} Y_{2 x} Sn_{1− x} O₄ with 0≤ x ≤0.5, and Ca_{1− y} Y_{2 y} Sn_{1− y} O₃ with 0≤ y ≤0.2 and 0.95≤ y ≤1.0 were found. The cell parameters of these solid-solution series were refined. The changes of rhombohedral cell parameters in the samples prepared in the range 0.565< y <0.714 of Ca_{1− y} Y_{2 y} Sn_{1− y} O₃ suggested the existence of solid solutions of Ca_0.4Y_1.2Sn_0.4O₃, although their single phases could not be prepared, except at y =0.6.     

Doping Effects of Ta on Conductivity and Microwave Dielectric Loss of MgTiO3 Ceramics

Two kinds of solid solution systems of Ta-doped MgTiO₃ were identified by X-ray diffraction, which can be represented by the formulae MgTi_{1− x} (Mg_1/3Ta_2/3) _x O₃ (0≤ x <0.5) and MgTi_{1− x} Ta _x O₃ (0≤ x <0.05). The conductivity and microwave dielectric loss for the two solid solution systems were examined by AC impedance and microwave resonator measurements, respectively. In the system MgTi_{1− x} (Mg_1/3Ta_2/3) _x O₃, the mechanism for the solid solution formation is the isovalent substitution of for Ti⁴⁺. In the system MgTi_{1− x} Ta _x O₃, the doping mechanism is the aliovalent substitution of Ta⁵⁺ for Ti⁴⁺, where for a small amount Ta doping, the oxygen vacancies formed during the high-temperature preparation are filled by an extra oxygen introduced from Ta₂O₅ and further Ta doping leads to an increase in the contents of and electrons, which was consistent with conductivity measurements. In both systems, the Q × f values improved, e.g., ∼17% for the isovalent substitution at x =0.08 and ∼10% for the aliovalent substitution at x =0.02. The filling oxygen vacancy and the substitution of Ta/Mg for Ti may contribute to the improvement of Q × f values for both systems.     

Visible Light-Sensitive InTaO4-Based Photocatalysts for Organic Decomposition

The ability of InTa_{1− x} V _x O₄ ( x =0, 0.002, 0.005, 0.01) and InTaO_{4− y} N _y ( y =0, 0.048, 0.059) powders to photocatalyze the oxidative decomposition of gaseous 2-propanol (IPA) when irradiated by the same number of visible or ultraviolet photons was confirmed. The first-principle calculations of InTa_0.875V_0.125O₈ indicated that the V 3d introduced state was discretely situated below the conduction band, which was composed mainly of Ta 5d. Similar calculations of InTaO_3.5N_0.5 indicated that the N 2p state was above the valence band, which was composed of O2p. These discrete narrow bands were responsible for the visible light sensitivity in the V- or N-doped InTaO₄ compounds.     

Phase Relations in the Pyrochlore-Rich Part of the Bi2O3−TiO2−Nd2O3 System

In this study we used solid-state synthesis to determine the phase relations in the pyrochlore-rich part of the Bi₂O₃−TiO₂−Nd₂O₃ system at 1100°C. The samples were analyzed using X-ray powder diffraction and scanning electron microscopy with energy- and wavelength-dispersive spectroscopy. A single-phase pyrochlore ceramic was obtained with the addition of 4.5 mol% of Nd₂O₃. We determined the solubility limits for the three solid solutions: (i) the pyrochlore solid solution Bi_{(1.6–1.08 x )}Nd _x Ti₂O_{(6.4+0.3 x )}, where 0.25< x <0.96; (ii) the solid solution Bi_{4− x} Nd _x Ti₃O₁₂, where 0< x <2.6; and (iii) the Nd_{2− x} Bi _x Ti₂O₇ solid solution, where 0< x <0.35. The determined phase relations in the pyrochlore-rich part are presented in a partial phase diagram of the Bi₂O₃−TiO₂−Nd₂O₃ system in air at 1100°C.     

Surface Morphologies of Magnesium Vanadium Oxide, Mg2-xV1+xO4

The microscopic appearance of the particle surfaces of magnesium vanadium oxide, Mg_2-xV_1+xO ₄ , loose powders prepared in various atmospheres at 1200°C was studied. The surface morphology, observed by SEM, was dependent on the V⁴⁺ content, and three typical features were distinguished at the following x values:

• (1) 

  0.75≤ x <1.00; rounded crystals with smooth surfaces
• (2) 

  0.55≤ x ≤0.75; edged crystals with stepped surfaces
• (3) 

  x ≤0.55; coarse crystals with rough surfaces

     

Syntheses and Unit-Cell Determination of Ba3V4O13 and Low-and High-Temperature Ba3P4O13

The syntheses and the results of unit-cell determinations ofBa₃V₄O₁₃ and the two forms (low- and high-temperature) of Ba₃P₄O₁₃ are presented. Ba₃V₄O₁₃ crystallizes in the monoclinic system, space group Cc or C2/c with unit-cell dimensions a=16.087, b=8.948, c=10.159 (x10nm), β=114.52° Low-Ba₃P₄O₁₃ crystallizes in the triclinic system, space group P1 or P1 with unit-cell dimensions a=5.757, b=7.243, c=8.104 (x10 nm) α=82.75°, β=73.94°, γ=70.71°. Low-Ba₃P₄O₁₃ transforms at 870°C into high-Ba₃P₄O₁₃ which crystallizes in the orthorhombic system, space group Pbcm (No. 57) (or Pbc2, No. 29) with unit-cell dimensions a =7.107, b=13.883, c=19.219 (x10 nm). No relations have been found between the structures of the tribarium tetravanadate and the tribarium tetraphosphate.