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1.
Interstitial titanium-chromium oxynitrides in the solid solution series Ti1− z Cr z (O x N y ) ( z = 0.2, 0.4, 0.5, 0.6, 0.8) have been obtained by ammonolysis of the TiO2 /Cr2 O3 precursors resulting from the coprecipitation method. The precursors and the resulting oxynitrides were characterized by auger electron spectroscopy, X-ray diffraction analysis, electron probe microanalysis, transmission electron microscopy, and BET surface area techniques. Compounds in the Ti1− z Cr z (O x N y ) series are prepared as single phases by nitridation at 1073 K for 8 h. The as-synthesized oxynitride powders contain only Ti1− z Cr z (O x N y ) with cubic structure and the particle size is in the nanometer scale. 相似文献
2.
Toshiya Hirata 《Journal of the American Ceramic Society》2000,83(12):3205-3207
Based on the virtual crystal approximation (or Vegard's law), the bond lengths of Ti1− x Sn x O2 were deduced from those of TiO2 and SnO2 , to allow the oxygen position and octahedral distortion to be determined as a function of x . The oxygen positional parameter ( u ) increased linearly when the Sn4+ cation (which has a larger ionic radius) was substituted for the Ti4+ cation, whereas the octahedral distortion exhibited a nonlinear decay with increasing x in Ti1− x Sn x O2 . At the same time, the bond-valence parameter, which relates bond valence to bond length, so that the central atom in the octahedron can retain a constant valence of +4.0, exhibited a correlation with u for Ti1− x Sn x O2 . The present results indicate that the different phonon/physical properties of TiO2 and SnO2 and/or their dependence on x in Ti1− x Sn x O2 can be associated with different octahedral distortions. 相似文献
3.
Guangxiu Cao Yaogang Li Qinghong Zhang Hongzhi Wang 《Journal of the American Ceramic Society》2010,93(1):25-27
La-doped TiO2− x F x (La–TiO2− x F x ) powders were prepared by the sol–gel method. X-ray diffraction results showed that La efficiently inhibited grain growth. X-ray photoelectron spectroscopy spectra revealed that La2 O3 and O–Ti–F bonds have formed, the La2 O3 maintained the high surface area of TiO2− x F x after calcination at a temperature above 500°C, while the O–Ti–F bonds increased the oxidation potential of the photogenerated hole in the valence band. The UV-vis spectroscopy of the La–TiO2− x F x showed that the presence of intraband gap states was likely responsible for its absorption of visible light. When the molar ratios of La and F to Ti were 1.5:100 and 5:100, respectively, and calcined at 500°C, the photocatalytic degradation rate of methylene blue over La–TiO2− x F x was about 1.5 times higher than that of F-doping TiO2 . 相似文献
4.
Jiann Shieh Hsiao Lei Wang Ming Shyong Tsai Min Hsiung Hon 《Journal of the American Ceramic Society》2002,85(3):636-640
Titanium nitride (TiN), titanium carbide (TiC), and titanium carbonitride (TiC x N1−x ) were prepared by plasma-enhanced chemical vapor deposition. A graded interlayer was introduced to explore its effects on the texture of the TiC and TiN. The results showed that the topography of the TiC x N1−x , which resembled coffee beans, resulted from a twinning core structure that caused the dendritic grain shape and enhanced the 〈211〉 texture of TiC0.62 ·N0.38 and TiC0.75 ·N0.25 . As graded coating was used as a transition layer, the texture of TiC was changed from (220) to (200), and TiN was changed from (200) to (220) due to the pseudomorphic forces provided by the first layer plus graded layer. The residual stress contributions to this phenomenon are also discussed. 相似文献
5.
pela Kunej Sreo D. kapin Danilo Suvorov 《Journal of the American Ceramic Society》2009,92(10):2373-2377
In this study we used solid-state synthesis to determine the phase relations in the pyrochlore-rich part of the Bi2 O3 −TiO2 −Nd2 O3 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 Nd2 O3 . We determined the solubility limits for the three solid solutions: (i) the pyrochlore solid solution Bi(1.6–1.08 x ) Nd x Ti2 O(6.4+0.3 x ) , where 0.25< x <0.96; (ii) the solid solution Bi4− x Nd x Ti3 O12 , where 0< x <2.6; and (iii) the Nd2− x Bi x Ti2 O7 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 Bi2 O3 −TiO2 −Nd2 O3 system in air at 1100°C. 相似文献
6.
Subsolidus phase relationships in the Ga2 O3 –Al2 O3 –TiO2 system at 1400°C were studied using X-ray diffraction. Phases present in the pseudoternary system include TiO2 (rutile), Ga2−2 x Al2 x O3 ( x ≤0.78 β-gallia structure), Al2−2 y Ga2 y O3 ( y ≤0.12 corundum structure), Ga2−2 x Al2 x TiO5 (0≤ x ≤1 pseudobrookite structure), and several β-gallia rutile intergrowths that can be expressed as Ga4−4 x Al4 x Ti n −4 O2 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. 相似文献
7.
The high-temperature equilibrium electrical conductivity of Ce-doped BaTiO3 was studied in terms of oxygen partial pressure, P (O2 ), and composition. In (Ba1−x Ce x )TiO3 , the conductivity follows the −1/4 power dependence of P (O2 ) at high oxygen activities, which supports the view that metal vacancies are created for the compensation of Ce donors, and is nearly independent of P (O2 ) where electron compensation prevails at low P (O2 ). When Ce is substituted for the normal Ti sites, there is no significant change in conductivity behavior compared with undoped BaTiO3 , indicating the substitution of Ce as Ce4+ for Ti4+ in Ba(Ti1−y Ce y )O3 . The Curie temperature ( T c ) was systematically lowered when Ce3+ was incorporated into Ba2+ sites, whereas the substitution of Ce4+ for Ti4+ sites resulted in no change in this parameter. 相似文献
8.
9.
New titanium–niobium oxynitride (Ti1− z Nb z O x N y ) powders were synthesized by ammonolysis of nanosized TiO2 /Nb2 O5 composite powders at 700°–900°C for 5 h. The products were characterized by X-ray diffraction (XRD), chemical analysis, and transmission electron microscopy. The results indicated that the as-synthesized powders were pure cubic structures with sizes of 30–60 nm. With increasing value of z , XRD peaks of Ti1− z Nb z O x N y powders tended to shift toward low 2θ angle and the cell parameter showed a linear increase. 相似文献
10.
Pavel Diko Paul.-H. Duvigneaud Alain Lanckbeen ré Van Moer Georges Naessens Robert Deltour 《Journal of the American Ceramic Society》1993,76(11):2859-2864
Porosity, grain growth, phase composition, and microstructural defects were studied in sintered YBa2 (Cu1−x )3 O7−x ceramics for x values up to 0.3. The porosity of the samples, related to the sintering mechanism, was independent of iron concentration. A linear dependence of the grain size with the inverse of the iron concentration was found, strongly suggesting grain boundary segregation of iron. The solubility limit was estimated to be x = 0.18 at 950°C in O2 . Beyond this limit, a new microstructural component was found consisting of YBa2 (Cu1−x Fex )3 O7−δ , YBaCuFeO5 and Ba(Cu,Fe)O2 . The transition from an orthorhombic twin to an orthorhombic tweed phase and a tetragonal phase was detected by polarized light microscopy. 相似文献
11.
Dong-Wan Kim Kyung Hyun Ko Do-Kyun Kwon Kug Sun Hong 《Journal of the American Ceramic Society》2002,85(5):1169-1172
(1− x )ZnNb2 O6 · x TiO2 ceramics were prepared using both anatase and rutile forms of TiO2 . At a composition of x = 0.58, a mixture region of ixiolite (ZnTiNb2 O8 ) and rutile was observed and the temperature coefficient of resonant frequency (τf ) was ∼0 ppm/°C. We found that although ɛr and τf were comparable, the quality factor ( Q × f , Q ≈ 1/ tan δ, f = resonant frequency) of 0.42ZnNb2 O6 ·0.58TiO2 prepared from anatase and rutile was 6000 and 29 000, respectively. The origin of the difference in Q × f of both samples was investigated by measuring electrical conductivity and by analysis of the anatase–rutile phase transition. The anatase-derived sample had higher conductivity, which was related to the reduction of Ti4+ . It is suggested that the increase of dielectric loss originates from an increase in Ti3+ and oxygen vacancies due to an anatase–rutile phase transition. 相似文献
12.
Lamrath Abdul Khalam Sherin Thomas Mailadil T. Sebastian 《International Journal of Applied Ceramic Technology》2007,4(4):359-366
The columbites MgNb2 O6 , MgTa2 O6 , and corundum-type Mg4 Nb2 O9 ceramics were prepared by the conventional solid-state ceramic route. The structure and microstructure of the sintered samples were investigated by X-ray diffraction and scanning electron microscopic techniques. The microwave dielectric properties of the samples were measured by the resonance method in the frequency range 4–6 GHz. The dielectric properties have been tailored by forming a solid solution between MgNb2 O6 and MgTa2 O6 and by the substitution of TiO2 for Nb2 O5 in both MgNb2 O6 and Mg4 Nb2 O9 ceramics. The Mg(Nb0.7 Ta1.3 )O6 has ɛr =29, Q u × f =67 800 GHz, and τf =0.8 ppm/°C and the MgO–(0.4)Nb2 O5 –(1.5)TiO2 composition has ɛr =34.5, Q u × f =81 300 GHz, and τf =−2 ppm/°C. 相似文献
13.
Grain-oriented Bi0.5 (Na0.85 K0.15 )0.5 TiO3 -Pb(Zr1− x Ti x )O3 (BNKT-PZT) ceramics were prepared via the reactive templated grain growth method, using platelike Bi4 Ti3 O12 particles. Factors that determine the degree of orientation were examined. Prereacted PZT gave a larger degree of orientation than PZT raw materials (PbO, ZrO2 , and TiO2 ) in the 75BNKT-25PZT ( x = 0.5) system. Increases in the titanium concentration in the PZT of the 75BNKT-25PZT system and in the BNKT concentration in the y BNKT-(100 − y )PZT ( x = 0.5) system increased the degree of orientation. The direction of material transport between BNKT and PZT was important to obtain ceramics with a large degree of orientation. 相似文献
14.
In the course of searching environmental friendly lead-free relaxor ferroelectrics a complete phase diagram of barium zirconate titanate, Ba(Zr x Ti1− x )O3 system with compositions 0.00≤ x ≤1.00 has been developed based on their dielectric behavior. It has been shown that BaZr x Ti1− x O3 system depending on the composition, successively depicts the properties extending from simple dielectric (pure BaZrO3 ) to polar cluster dielectric, relaxor ferroelectric, second order like diffuse phase transition, ferroelectric with pinched phase transitions and then to a proper ferroelectric (pure BaTiO3 ). A comprehensive structure–property correlation of BaZr x Ti1− x O3 ceramics has been studied to understand the various ferroelectric phenomena in the whole phase diagram. 相似文献
15.
TERRENCE B. LINDEMER ALFRED L. SUTTON Jr. 《Journal of the American Ceramic Society》1988,71(7):553-561
The extensive nonstoichiometry in the 〈U1– z Gd z O2± x 〉 † phase was investigated experimentally and the data are represented by a chemical thermodynamic method. The experimental ranges of temperature, oxygen potential, and z were 1273 to 1773 K, 0 to −600 kJ/mol, and 0.1 to 0.8, respectively. For hypostoichiometry, ideal-solution thermodynamics for the equilibrium 3Gd4/3 O2 + 4UO2 + (O2 ) = 6U2/3 Gd2/3 O8/3 were used to represent the experimental data, while for hyperstoichiometry a nonideal solution was used for the equilibrium 4UO2 + (O2 ) = 2U2 O5 . The wide ranges in x and z led to an improvement of the previous analysis of literature data and led to partial molal Gibbs free energy values that are useful for any thermodynamic calculation involving the phase. 相似文献
16.
The presence of TiC or TiN paritcles in an Al2 O3 matrix affects the thermal stability of the composites in oxidizing environments. In isothermic oxidation tests at 700°, 800°, 900°, 1000°, and 1100°C for up to 20 h, two different oxidation regimes have been observed at T < 900°C and at 900°C ≤ T ≤ 1100°C. At low temperatures ( T < 900°C), the oxidation follows a phase-boundary reaction; the reaction product initially consists of aggregates of submicrometer needlelike TiO2 rutile crystals that subsequently grow and coalesce. When a continuous TiO2 rutile layer is formed ( T ≥ 900°C), the oxidation kinetics change to parabolic, and the diffusion of O2 through a thick TiO2 layer is proposed as the governing step. 相似文献
17.
HIROTOSHI OSHIMA 《Journal of the American Ceramic Society》1980,63(9-10):504-508
Phase relations in the quasi-ternary system MgO-V2 O3 -VO2 at 1200°C were studied using the quenching technique under controlled O2 atmospheres. A new phase of a type z VO y Mg2− x V1+ x O4 (0< x <1, y ≥1.5, z >0) was found with a compositional region along the MgV2 O4 -Mg2 VO4 join. Equilibrium P O 2 observed for Mg2− x V1+ x O4 is quite different from that for V n O2 n -1 with an equal ratio of V3+ /V4+ , corresponding to the V3+ stabilities in two types of compounds. Thus, the phase relations in the ternary system were constructed on a conventional triaxial diagram as a function of P O2 . 相似文献
18.
The effect of the addition of V2 O5 on the structure, sintering and dielectric properties of M -phase (Li1+ x − y Nb1− x −3 y Ti x +4 y )O3 ceramics has been investigated. Homogeneous substitution of V5+ for Nb5+ was obtained in LiNb0.6(1− x ) V0.6 x Ti0.5 O3 for x ≤ 0.02. The addition of V2 O5 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 τf = 11 ppm/°C. Preliminary investigations suggest that silver metallization does not diffuse into the V2 O5 -doped M -phase ceramics at 900°C, making these materials potential candidates for low-temperature cofired ceramic (LTCC) applications. 相似文献
19.
A narrow region of Zn-vacancy-containing cubic perovskites was formed in the (1− x )Ba3 (ZnNb2 )O9 −( x )Ba3 W2 O9 system up to 2 mol% substitution ( x =0.02). The introduction of cation vacancies enhanced the stability of the 1:2 B-site ordered form of the structure, Ba(Zn1− x □ x )1/3 (Nb1− x W x )2/3 O3 , which underwent an order–disorder transition at 1410°C, ∼35° higher than pure Ba(Zn1/3 Nb2/3 )O3 . The Zn vacancies also accelerated the kinetics of the ordering reaction, and samples with x =0.006 comprised large ordered domains with a high lattice distortion ( c/a =1.226) after a 12 h anneal at 1300°C. The tungstate-containing solid solutions can be sintered to a high density at 1390°C, and the resultant ordered ceramics exhibit some of the highest microwave dielectric Q factors ( Q × f =1 18 000 at 8 GHz) reported for a niobate-based perovskite. 相似文献
20.
Additions of NiO, CoO, MnO2 , Fe2 O3 , and CuO promote the anatase-rutile transformation and grain growth of TiO2 . Additions of Na2 O and WO3 retard the transformation and have no effect on the grain growth. The addition of MoO3 strongly promotes the grain growth but has only a slight effect on the phase transformation. Both the grain growth and transformation are promoted slightly by Cr2 O3 . The transformation is significantly affected by the method of preparing TiO2 . The grain size of TiO2 heated in H2 exceeds that of TiO2 heated in O2 , in air, in argon, and in vacuum. The rate of transformation decreases with an increase in the partial pressure of oxygen of the atmosphere. 相似文献