共查询到20条相似文献,搜索用时 31 毫秒
1.
Hongwu Xu Alexandra Navrotsky Mari Lou Balmer Yali Su Eric R. Bitten 《Journal of the American Ceramic Society》2001,84(3):555-560
Enthalpies of drop solution for a suite of substituted pollucites with the compositions CsTi x Al1− x Si2 O6+0.5 x , 0 ≤ x ≤ 1, which are synthesized using the sol–gel method, have been measured in molten lead borate (2PbO·B2 O3 ) at 701°C. As Ti4+ substitutes for Al3+ , the enthalpies of drop solution become less endothermic and show exothermic heats of mixing within the composition range from x = 0.3 to 1. This nonideal mixing behavior is consistent with the trend seen in variation of lattice parameters, and we interpret it to be a result of the short-range order associated with the framework cations Al3+ , Si4+ , and Ti4+ in the structure. Using enthalpies of drop solution of SiO2 , Al2 O3 , TiO2 , and Cs2 O, standard molar enthalpies of formation of these phases from their constituent oxides and from the elements are derived for the first time. 相似文献
2.
Subsolidus phase relationships in the Ga2 O3 –In2 O3 –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 Ga2 O3 ( ss ), In2 O3 ( ss ), SnO2 , Ga3− x In5+ x Sn2 O16 , and several intergrowth phases that can be expressed as Ga4−4 x In4 x Sn n −4 O2 n −2 where n is an integer. An In2 O3 –SnO2 phase and Ga4 SnO8 form at 1375°C but are not stable at 1250°C. GaInO3 did not form over the temperature range 1000–1400°C. 相似文献
3.
Takayuki Komatsu Michiko Ueta Tomohiro Ohki Ryuji Sato Kazumasa Matusita 《Journal of the American Ceramic Society》1992,75(7):1864-1869
The Ba-doped superconducting (Bi,Pb)2 Sr2- x Ba x Ca2 Cu3 O y and (Bi,Pb)2 Sr2 Ca2- x Ba x Cu3 O y (0 ≦ x ≦ 1.0) were prepared by using a melt-quenching method, and the effect of Ba additions on the glass-forming ability and the crystalline phase was examined. The glass-forming ability was not improved by substitution of Ba for Sr or Ca, and particularly BaPbO3 as well as CaO was observed in the melt-quenched sample of (Bi,Pb)2 SrBaCa2 Cu3 O y . BaPbO3 crystals were precipitated in all glass-ceramics with Ba substituted for Sr or Ca. The partial substitution of Ba substituted for Sr was effective for the formation of the high- T c phase, and (Bi,Pb)2 Sr1.4 Ba0.6 Ca2 Cu3 O y glass-ceramics obtained by annealing at 830°C for 100 h exhibited superconductivity with a T c of 103 K, although BaPbO3 and the low- T c phase were still largely present. 相似文献
4.
Tsuyoshi Honma Yasuhiko Benino Takumi Fujiwara Takayuki Komatsu Ryuji Sato 《Journal of the American Ceramic Society》2005,88(4):989-992
The glass formation region, crystalline phases, second harmonic (SH) generation, and Nd:yttrium aluminum garnet (YAG) laser-induced crystallization in the Sm2 O3 –Bi2 O3 –B2 O3 system were clarified. The crystalline phases of Bi4 B2 O9 , Bi3 B5 O12 , BiBO3 , Sm x Bi1− x BO3 , and SmB3 O6 were formed through the usual crystallization in an electric furnace. The crystallized glasses consisting of BiBO3 and Sm x Bi1− x BO3 showed SH generations. The formation of the nonlinear optical BiB3 O6 phase was not confirmed. The formation (writing) region of crystal lines consisting of Sm x Bi1− x BO3 by YAG laser irradiation was determined, in which Sm2 O3 contents were∼10 mol%. The present study demonstrates that Sm2 O3 –Bi2 O3 –B2 O3 glasses are promising materials for optical functional applications. 相似文献
5.
The electrical properties of Sr0.5 Ba0.3 TiO3 in the presence of Nb2 O5 as a donor, 3Li2 O · 2SiO2 as a sintering agent, and Bi2 O3 as a dopant have been studied. When the compositions of the ceramics were 1 mol Sr0.7 Ba0.3 TiO3 + 0.5 mol% Nb2 O5 + 2 mol% 3Li2 O · 2SiO2 + 0.2 mol% Bi2 O3 , the ceramics were sintered at 1100°C and exhibited the following characteristics: apparent dielectric constant ɛ, 25000; loss factor tan δ, 2%; insulating resistivity ρj , 1010 Ω· cm; variation of dielectric constant with temperature Δɛ/ɛ (−25° to +85°C), +10%, −14%. ɛ and tan δ show only small changes with frequency. The study shows this ceramic can be used in multilayer technology. 相似文献
6.
Stephan Senz reas Graff Werner Blum Dietrich Hesse Hans-Peter Abicht 《Journal of the American Ceramic Society》1998,81(5):1317-1321
Fresnoite grows at 700° and 800°C, and Ba6 Ti7 O40 grows at 1200°C with definite orientations, which are determined by X-ray diffraction pole figure analysis. Partially textured fresnoite is formed at higher temperatures. The SiO2 films react with the BaTiO3 crystals, forming the phases Ba2 TiSi2 O8 (fresnoite) and Ba6 Ti17 O40 . At 700° and 800°C, both phases grow with definite orientations, which are determined by X-ray diffraction pole figure analysis. Partially textured polycrystalline phases are formed at higher temperatures. 相似文献
7.
The solid-state reaction of SrNb2 O6 and BaNb2 O6 to form Sr x Ba1− x Nb2 O6 (SBN) at different temperatures and heating rates was investigated. The reaction kinetics were analyzed by X-ray diffractometry for quenched samples, and the internal-standard method was applied to quantify the extent of the reaction. A nonisothermal kinetic empirical model was proposed to evaluate the activation energy and rate constant of SBN with different Sr:Ba ratios. It was found that the kinetic form would change above and below a transition at a reaction fraction of ∼60%, which might be due to the change of the frequency factor. It was also verified that the model that was presented was more favorable to describe the nonisothermal reaction kinetics of SBN. 相似文献
8.
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
9.
Steven A. Markgraf Shiv K. Sharma Amar S. Bhalla 《Journal of the American Ceramic Society》1992,75(9):2630-2632
Raman spectra are reported for fresnoite (Ba2 Ti(Si,Ge)2 O8 glasses, and comparison is made between the Raman spectra of the corresponding crystalline powders and glasses of Ba2 TiSi2 O8 and Ba2 TiGe2 O8 . The Ba2 TiGe2 O8 glass spectra show correspondence with the Ba2 TiGe2 O8 crystalline Raman spectra; the v s (Ge–O–Ge) mode occurs at 518 cm−1 in the glass and at 521 cm−1 in the crystalline material. Five-fold coordinated titanium is the majority species present in the Ba2 TiGe2 O8 glass as revealed by a strong band at 824 cm−1 in the I glass spectrum. The Ba2 TiSi2 O8 glass spectra are similar to the Ba2 TiSi2 O8 crystalline spectrum; the strongest band is found at 836 cm−1 in the I glass spectrum. Through comparison with the previous Raman data of other titania silicate glasses, we conclude that the Ba2 TiSi2 O8 glass has a structure similar to the crystalline phase. 相似文献
10.
Ni Qin Marjeta Maek Krmanc Danilo Suvorov 《Journal of the American Ceramic Society》2008,91(8):2593-2600
K x Ba1− x Ga2− x Ge2+ x O8 (0.6≤ x ≤1) polycrystalline ceramics are potential materials for glass-free low-temperature cofired ceramics (LTCC) substrates. We have made a comprehensive study of the kinetics of the monoclinic-to-monoclinic P 21 / a ⇔ C 2/ m phase transition. The low-temperature-stable P 21 / a phase with a high Q × f value was synthesized using a subsolidus method and was well sintered at the LTCC temperature with a H3 BO3 additive. A good combination of low sintering temperature (910°–920°C), high Q × f values (96 700–104 500 GHz), low permittivities (5.6–6.0), and a small temperature coefficient of resonant frequency (∼−20 ppm/°C) was obtained for ceramics with x =0.67 and 0.9 and with 0.1 wt% of H3 BO3 . 相似文献
11.
Tae-Jin Park Mark J. Davis Paula Vullo Tina M. Nenoff James L. Krumhansl Alexandra Navrotsky 《Journal of the American Ceramic Society》2009,92(9):2053-2058
Barium titanosilicates are possible oxide forms for the immobilization of short-lived fission products in radioactive waste. Ba2 TiSi2 O8 (fresnoite) and BaTiSiO5 (Ba-titanite) samples were prepared by a solid-state synthesis. The enthalpies of formation of Ba2 TiSi2 O8 crystal and glass at 25°C and of BaTiSiO5 glass were obtained from drop solution calorimetry in a molten lead borate (2PbO–B2 O3 ) solvent at 701°C. The enthalpy of formation for fresnoite composition samples from constituent oxides was exothermic and became more exothermic with increasing crystallinity. Differential scanning calorimetry revealed that the crystallization rate of the fresnoite glasses increased with increasing devitrification. A modified Product Consistency Test-Procedure B (PCT-B) was used to collect solubility data on the fresnoite and titanate phases. The tests suggest that both glassy and crystalline fresnoite exhibit favorable aqueous stability and should be explored further as radioactive waste forms for long-term storage. 相似文献
12.
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 Sm8+2 x Ti18 O54 solid solution ( x = 2/3). A small amount of tin substitution for titanium improved the temperature coefficient of resonant frequency (τf ) but led to a decrease of the relative dielectric constant (ɛ) and the quality factor ( Qf ). The Ba6−3 x Sm8+2 x (Ti1− z Snz )18 O54 -based tungsten-bronze phase became unstable for compositions with a tin content of ≥10 mol%, where BaSm2 O4 and Sm2 (Sn,Ti)2 O7 appeared, 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 τf . Excellent microwave dielectric properties were achieved in Ba6−3 x (Sm1− y Nd y )8+2 x (Ti1− z Sn z )18 O54 ceramics with y = 0.8 and z = 0.05 sintered at 1360°C for 3 h: ɛ= 82, Qf = 10 000 GHz, and calculated τf =+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. 相似文献
13.
Hongwu Xu Alexandra Navrotsky M. Lou Balmer Yali Su 《Journal of the American Ceramic Society》2002,85(5):1235-1242
The crystal structures for a suite of substituted pollucites with the compositions CsTi x Al1– x Si2 O6+0.5 x , 0 ≤ x ≤ 1, have been determined from Rietveld analysis of powder synchrotron XRD data. Our results indicate that the pollucite end member (CsAlSi2 O6 ) has a tetragonal structure (space group I 41 / a ), whereas all other compositions are cubic (space group Ia 3 d ). The increased symmetry for the titanium-substituted structures is presumably due to the incorporation of additional O2− anions (needed for compensating the charge imbalance between Ti4+ and Al3+ ), which effectively holds open the expanded cubic framework. In situ cooling experiments of the substituted phase CsTi0.1 Al0.9 Si2 O6.05 reveal a displacive transformation to the tetragonal structure at ∼230 K. This transformation is tricritical in nature and is analogous to the tetragonal-to-cubic transition in pollucite on heating. 相似文献
14.
Two cubic pyrochlore phases exist in the system ZnO–Bi2 O3 –Sb2 O5 . Neither has the supposed "ideal" stoichiometry, Zn2 Bi3 Sb3 O14 . One, P 1 , is a solid solution phase, Zn2+ x Bi2.96−( x − y ) Sb3.04− y O14.04+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, Zn2 Bi3.08 Sb2.92 O13.92 with a =10.462(2) Å. Subsolidus phase relations at 950°C involving phases P 1 and P 2 in the ZnO–Bi2 O3 –Sb2 O5 phase diagram have been determined. 相似文献
15.
Anita Fossdal Mari-Ann Einarsrud Tor Grande 《Journal of the American Ceramic Society》2005,88(7):1988-1991
The phase relations in the pseudo-ternary system La2 O3 –SrO–Fe2 O3 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 O3 n +1−δ ( n =1, 2, 3, and ∞) and Sr1− x La x Fe12 O19 , while only limited solubility of La in Sr4− z La z Fe6 O13±δ was observed. At high Fe2 O3 content, a liquid with low La2 O3 content was stable at 1300°C. 相似文献
16.
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
17.
JOHN B. HARDAWAY III JOHN W. PATTERSON D. R. WILDER JON D. SCHIELTZ 《Journal of the American Ceramic Society》1971,54(2):94-98
The emf method was used to determine the lower limit of oxygen activity for essentially pure anionic conduction in Th0.85 Y0.15 O1.925 from 775° to 1000C. The results show that the oxygen transference number is ≥0.99 when log PO 2 ≥−6.5(104 / T °K)+29. 相似文献
18.
Piezoelectric ceramics Na1− x Ba x Nb1− x Ti x O3 with low BaTiO3 concentrations x have been prepared by the solid-state reaction method, and their ferroelectric and piezoelectric properties have been studied. The ceramics are classic ferroelectrics when x ≤0.10, and the ferroelectric–paraelectric phase transition becomes diffusive when x ≥0.15. A low doping level of BaTiO3 changes the NaNbO3 ceramics from antiferroelectric to ferroelectric. With the increase in BaTiO3 doping level, the Curie temperature of ceramics decreases linearly and the remnant polarization and coercive field also decrease, while their dielectric constant increases. Na0.9 Ba0.1 Nb0.9 Ti0.1 O3 ceramics show the largest piezoelectric constant d 33 (147 pC/N) and good sinterability, suggesting that it is a good candidate for lead-free piezoelectric ceramics. 相似文献
19.
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
20.
Fei Zhao Zhenxing Yue Jing Pei Hao Zhuang Zhilun Gui Longtu Li 《Journal of the American Ceramic Society》2007,90(8):2461-2466
Microwave dielectric ceramics with the composition of Ba[Ti1− x (Ni1/2 W1/2 ) x ]O3 ( x =0.4–0.6) were prepared by a solid-state reaction method. The evolution of the crystalline phases was investigated by X-ray powder diffraction analysis. A cubic-to-hexagonal phase transition occurred between 1000° and 1300°C. The phase transition is irreversible; thus, the hexagonal phase remains stable at room temperature. The X-ray powder diffraction data for x =0.5 were refined using the Rietveld method. It was identified as a h -BaTiO3 -type hexagonal perovksite with the space group of P 63 / mmc . It also reveals that random occupancy of Ti4+ and W6+ ions occurs in the B-site substructures, whereas Ni2+ ions exclusively occupy the octahedral site in the corner-sharing octahedron. The dielectric properties of dense-sintered ceramics were characterized at microwave frequencies. With an increase in x from 0.4 to 0.6, the Q × f value increased from 26 700 to 42 000 GHz, whereas ɛr decreased from 29.8 to 20.0, and τf from +6.5 to −9.9 ppm/°C. 相似文献