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1.
Sathi Rajachandran Nair Ram Dayal Purohit Avesh Kumar Tyagi Pankaj Kumar Sinha Beant Prakash Sharma 《Journal of the American Ceramic Society》2008,91(1):88-91
Ultrafine La(Ca)CrO3 (LCC) powder was prepared through the glycine–nitrate gel combustion process. It was shown for the first time that the use of relatively inexpensive CrO3 as a starting material for chromium has potential for the bulk preparation of sinter-active LCC powder. As-prepared powder, when calcined at 700°C, resulted in LCC along with a small amount of CaCrO4 . The calcined powder was found to be composed of soft agglomerates with a particle size of ≈70–290 nm. The cold pressing and sintering of the calcined powder at 1200°C resulted in the mono-phasic La0.7 Ca0.3 CrO3 with density ≈98% of its theoretical value. This is the lowest sintering temperature ever reported for La0.7 Ca0.3 CrO3 . The conductivity of the sintered La0.7 Ca0.3 CrO3 at 1000°C was found to be ≈57 S/cm in air. The sintering and electrical behavior achieved for La0.7 Ca0.3 CrO3 may find application as an interconnect material for high-temperature solid oxide fuel cells if problems with chemical expansion and poor conductivity in fuel can be overcome. 相似文献
2.
An all-alkoxide route to films and nano-phase powders of the La0.5 Sr0.5 CoO3 perovskite is described. To our knowledge, this is the first purely alkoxide-based route to (La1− x Sr x )CoO3 , and it yields phase-pure and elementally homogeneous perovskite at 700°C by heating at 2°C/min. At 700°C, a cubic unit cell was obtained with a c =3.853Å, and after further heating to 1000°C, a rhombohedral cell could be indexed: a r =5.417 Å, αr =59.94°. Ninety to 130 nm thick films of La0.5 Sr0.5 CoO3 were obtained by spin coating. The gel-to-oxide conversion was studied in some detail, using thermo-gravimetric analysis, differential scanning calorimetry, powder X-ray diffraction, IR spectroscopy, and transmission electron microscope equipped with an energy-dispersive X-ray spectrometer. 相似文献
3.
E. E. Boakye R. S. Hay P. Mogilevsky M. K. Cinibulk 《Journal of the American Ceramic Society》2008,91(1):17-25
Equiaxed yttrium–lanthanum phosphate nanoparticles (Y0.7 ,La0.3 )PO4 ·0.7H2 O were made and used to continuously coat Nextel™ 720 fiber tows. The particles were precipitated from a mixture of yttrium and lanthanum citrate chelate and phosphoric acid (H3 PO4 ), and characterized with differential thermal analysis and thermogravimetric analysis, X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. The coated fibers were heat treated at 1000°–1300°C for 1, 10, and 100 h. Coating grain growth kinetics and coated fiber strengths were determined and compared with equiaxed La-monazite coatings. The relationships between coating porosity, coating hermeticity, and coated fiber strength are discussed. 相似文献
4.
Phase equilibria of the La2 O3 -SrO-CuO system have been determined at 950°C and 10 kbar (1 GPa). Stable phases at the apices of the ternary phase diagram are CuO, La2 O3 , and SrO. Stable intermediate phases are La2 CuO4 in the LaO1.5 -CuO binary and Sr2 CuO3 , SrCuO2 , and Sr14 Cu24 O41 in the CuO-SrO binary. The La2-x Sr x CuO4-δ solid solution is stable where 0.0 ≤ x ≤ 1.3, the La2-x Sr1+x Cu2 O6+δ solid solution is stable where 0.0 ≤ x ≤ 0.2, the La8-x Sr x Cu8 O20-δ solid solution is stable where 1.3 ≤ x ≤ 2.7, the La x Sr14-x -Cu24 O41 solid solution is stable where 0 ≤ x ≤ 6, and the La1+x Sr2-x Cu2 O5.5+δ phase is stable where 0.04 ≤ x ≤ 0.16. The La2 O3 -SrO-CuO phase diagram at 950°C and 10 kbar is almost identical to that determined by other authors at 950°C and 1 atm, in terms of phase stability and solid-solution ranges. 相似文献
5.
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
6.
MADELEINE H. WARZEE MARCEL MAURICE FRANZ HALLA WALTER R. RUSTON 《Journal of the American Ceramic Society》1965,48(1):15-17
In the binary system PbO–Laz O3 only one compound, 4PbO.La2 O3 , exists; it is flanked by two eutectics. The structure of the compound, although of lower symmetry, is intimately related to the C modification of the rare earths. Below 800° to 1000°C, metastable solid solutions are formed from oxide mixtures coprecipitated from mixed solutions of the nitrates, the cubic parameter a = 5.66 A, if extrapolated to pure La2 O3 , corresponding to half the a parameter of the C form of La2 O3 . The solid solutions existing between the compositions La2 O3 –2Pb0 and pure La2 O3 have a cubic face–centered lattice and obey Vegard's rule. The systems of PbO with Sm2 O3 and Gd2 O8 are quite similar to that with La2 O3 . The compound Sm2 O3 .4Pb0 decomposes at 1000°C with evaporation of PbO; Sm2 O3 remains in the B modification. 相似文献
7.
Hideki Taguchi Daisuke Matsuda Mahiko Nagao Kimiaki Tanihata Yoshinari Miyamoto 《Journal of the American Ceramic Society》1992,75(1):201-202
Perovskite-type (La1- x Sr x )MnO3 (0 x 0.3) was synthesized through the sol–gel process at low temperature (400° to 500°C). Poly(acrylic acid) (PAA) was used to make a gel from an aqueous solution of lanthanum, strontium, and manganese nitrates. The particle-diameter distribution of the manganites had a maximum value of 0.3 to 0.7 μ m, and a specific surface area of about 17.5 to 23.5 m2 /g. 相似文献
8.
By a combination of conventional physical property measurements and high-temperature electrical property studies, the solid solution limit, transport parameters, and potential defect regimes of the Bi2.1 Sr1.9 (Ca1 - x Y x )Cu2 O y solid solution were established. A continuous solid solution extends to x = 0.7 or 0.8. The electrical properties indicate that the product of the hole density-of-states and mobility for semiconducting compositions is approximately an order of magnitude smaller than for the other p -type superconducting cuprates. A pronounced drop in hole concentration accompanies the tetragonal-to-orthorhombic transition at x = 0.5, whereafter superconductivity disappears. The electrical properties also indicate that a composition x change occurred reversibly below 1100°C. 相似文献
9.
The ternary phase diagram of Al2 O3 -La2 O3 -TiO2 at 1400°C was determined with 12 compatibility triangles. Al2 O3 stabilizes the A-site-deficient La2/3 TiO3 perovskite structure. According to XRD and microstructural investigations, the solid solution extends along the La2/3 TiO3 -LaAlO3 tie line from at least 4 mol% LaAlO3 to pure LaAlO3 . With increasing LaAlO3 content, the stabilized La2/3 TiO3 structure changes from orthorombic via tetragonal to cubic. 相似文献
10.
Maria P. Seabra Maxim Avdeev Victor M. Ferreira Rob C. Pullar Neil McN. Alford Ian M. Reaney 《Journal of the American Ceramic Society》2004,87(4):584-590
The microwave dielectric properties and microstructures of compounds in the solid solution series x BaTiO3 –(1− x )La(Mg1/2 Ti1/2 )O3 (BTLMT) have been investigated. The structural phase transitions that occur as a function of x have been studied and are related to changes in the dielectric properties. For compounds where x ≤ 0.1, X-ray diffraction (XRD) showed evidence of 1:1 ordering between Mg and Ti cations. For x ≤ 0.3, XRD and electron diffraction revealed that compounds were tilted in both antiphase and in-phase. However, for 0.3 < x < 0.7, only antiphase tilting was present. The temperature coefficient of resonant frequency (τf ) vs the relative permittivity (ɛr ) was linear until x = 0.5 at which point in the solid solution the transition to a nontilted structure resulted in nonlinear behavior. τf values close to zero (−2 ppm/°C) were achieved at x = 0.5 (ɛr ∼ 60), which had a quality factor ( Q · f o ) of 9600 GHz. 相似文献
11.
Sergey Kucheiko Dong-Hun Yeo Ji-Won Choi Seok-Jin Yoon Hyun-Jai Kim 《Journal of the American Ceramic Society》2002,85(5):1327-1329
The microwave dielectric properties of CaTi1− x (Al1/2 Nb1/2 ) x O3 solid solutions (0.3 ≤ x ≤ 0.7) have been investigated. The sintered samples had perovskite structures similar to CaTiO3 . The substitution of Ti4+ by Al3+ /Nb5+ improved the quality factor Q of the sintered specimens. A small addition of Li3 NbO4 (about 1 wt%) was found to be very effective for lowering sintering temperature of ceramics from 1450–1500° to 1300°C. The composition with x = 0.5 sintered at 1300°C for 5 h revealed excellent dielectric properties, namely, a dielectric constant (ɛr ) of 48, a Q × f value of 32 100 GHz, and a temperature coefficient of the resonant frequency (τf ) of −2 ppm/K. Li3 NbO4 as a sintering additive had no harmful influence on τf of ceramics. 相似文献
12.
Phase equilibria of the La2 O3 –SrO–CuO system have been determined at 950°C at 30 kbar (3 GPa). Stable phases at the apexes of the ternary phase diagram are CuO, La2 O3 , and SrO. Stable intermediate phases are La2 , CuO4 and La2 Cu2 O5 in the LaO1.5 –CuO binary and Sr2 CuO3 , SrCuO2 , and Sr14 Cu24 O41 in the CuO–SrO binary. The La2– x Sr x -CuO4–δ solid solution is stable for 0.00 is ≤ x ≤ 1.29, the La2– x Sr1+ x Cu2 O6+δ solid solution is stable for 0.03 ≤ x ≤0.20, the La2– x Sr x Cu2 O5–δ solid solution is stable for 0.00 ≤ x ≤1.08, and the La x Sr14– x Cu24 O41 solid solution is stable for 0.00 ≤ x ≤ 6.15. The 30 kbar phase diagram differs from the 1 atm (0.1 MPa) and 10 kbar (1 GPa) results principally in the absence of La1– x Sr2+ x Cu2 O5.5+δ as a stable phase and the extended range of the La2– x Sr x Cu2 O5–δ solid solution at 30 kbar. 相似文献
13.
Chai Zhang Liang Jing-Kui Xu Xian-ting 《Journal of the American Ceramic Society》1988,71(10):C436-C438
The phase diagram of the pseudobinary system Li2 SO4 –La2 (SO4 )3 has been investigated by means of X-ray diffraction and differential thermal analysis. LiLa(SO4 )2 is formed by a peritectic reaction in this system; the peritectic temperature is 653±3°C. The eutectic reaction of Li2 SO4 and LiLa(SO4 )2 occurs at 553±3°C; the composition at the eutectic point is 17 mol% La2 (SO4 )3 . LiLa(SO4 )2 is monoclinic with a=1.375 nm, b=0.6744 nm, c=0.7068 nm, and β=105.4°. The ionic conductivity of LiLa(SO4 )2 has been studied from room temperature to 350°C and is found to be relatively low at room temperature or at lower temperatures. Its activation energy is 0.66 eV. Thus it is not suitable as a fast ion conductor. 相似文献
14.
Composite ceramics in a solid solution of (Mg1− x Mn x )2 TiO4 ( x =0.02–0.1) have been prepared by the mixed oxide route. Formation of the solid solution was confirmed by the X-ray diffraction, the EDX analysis, and the measured lattice parameters, which varied linearly from Mg2 TiO4 ( a = b = c =8.4410 Å) to (Mg0.9 Mn0.1 )2 TiO4 ( a = b = c =8.4445 Å). The XRD analysis also confirmed the co-existence of a cubic-structured (Mg1− x Mn x )2 TiO4 and an ilmenite-structured second phase (Mg1− x Mn x )TiO3 . The composition expected to have a maximum Q × f (276 200 GHz at 10.5 GHz) is (Mg0.95 Mn0.05 )2 TiO4 with ɛr ∼15.69 and τf ∼−52.6 ppm/°C. The existence of the second phase, however, would lead to no significant variation in the dielectric properties of the specimen because it possesses compatible properties compared with that of the main phase. 相似文献
15.
Ceramic samples with the nominal composition (1− x ) BaTiO3 + x Ba3 Ti2 YO8.5 ( x =0−0.535) were prepared by the mixed oxide method. X-ray diffraction (XRD) analysis shows that the materials are of single phase with a cubic symmetry as x ≤0.16. The compositions of the solid solutions ( x ≤0.16) can be expressed equivalently as Ba(Ti1− y Y y )O3−δ ( y ≤0.122, y = x /(1+2 x )). For x >0.16, the materials are diphasic composites consisting of Ba(Ti1− y Y y )O3 ( y =0.122) and Ba3 Ti2 YO8.5 . The microstructure observation by scanning electron microscopy supports the XRD result. The dielectric behavior and phase transitions of the solid solutions ( x ≤0.16) vary with different Y concentrations. The dielectric constant of the composites ( x >0.16) follows approximately the Lichteneker relation in a wide temperature range. 相似文献
16.
Rejini Rajamma Mailadil Thomas Sebastian 《Journal of the American Ceramic Society》2007,90(8):2472-2475
The microwave dielectric properties of two A-site-deficient perovskite-type ceramics in the La6 Mg4 A2 W2 O24 [A=Ta and Nb] system were investigated. The compounds were synthesized by the solid-state ceramic route. The structure and microstructure were analyzed using X-ray diffraction and scanning electron microscopy techniques. The dielectric properties were measured in the microwave frequency range [4–6 GHz] by the resonance method. La6 Mg4 Ta2 W2 O24 had Q u × f =13 600 GHz, ɛr =25.2, and τf =−45 ppm/°C and La6 Mg4 Nb2 W2 O24 had Q u × f =16 400 GHz, ɛr =25.8, and τf =−56 ppm/°C. 相似文献
17.
Zhong Zhuang Xian Ping Wang Dan Li Tao Zhang Qian Feng Fang 《Journal of the American Ceramic Society》2009,92(4):839-844
Dense, crack-free, and uniform La2 Mo2− x W x O9 ( x =0, 0.1, and 0.2) nanocrystalline films were successfully synthesized on poly-alumina substrates via a modified sol–gel method, with inorganic salt of La(NO3 )3 ·6H2 O, (NH4 )6 Mo7 O24 ·4H2 O, and (NH4 )6 H2 W12 O24 as precursors. Pure La2 Mo2 O9 phase was confirmed by X-ray diffractometer when the annealing temperature was >500°C. The average grain size of the La2 Mo2− x W x O9 films is in the range of 90–400 nm, depending upon the conditions of thermal treatment, and the thickness of films can reach 1 μm by repetitive spin-coating. The electrical conductivity increases with decreasing grain size and reaches 0.074 S/cm at 600°C in the film with a grain size of 90 nm, which is one order of magnitude higher than that in the corresponding bulk materials. W-doping can suppress the phase transition that occurs at 580°C in pure La2 Mo2 O9 and enhance the low-temperature ionic conductivity. Furthermore, the activation energy of conductivity in the nanocrystalline La2 Mo2 O9 films decreases to about 0.6 eV in comparison with 1.0 eV in the bulk ones, which implies that the grain resistance prevails in the total resistance, when grain size reduces to nanometer domain. 相似文献
18.
ROBERT RUH K. S. MAZDIYASNI P. G. VALENTINE H. O. BIELSTEIN 《Journal of the American Ceramic Society》1984,67(9):190-C
Subsolidus phase relations in the low-Y2 O3 portion of the system ZrO2- Y2 O3 were studied using DTA with fired samples and X-ray phase identification and lattice parameter techniques with quenched samples. Approximately 1.5% Y2 O3 is soluble in monoclinic ZrO2 , a two-phase monoclinic solid solution plus cubic solid solution region exists to ∼7.5% Y2 O3 below ∼500°C, and a two-phase tetragonal solid solution plus cubic solid solution exists from ∼1.5 to 7.5% Y2 O3 from ∼500° to ∼1600°C. At higher Y2 O3 compositions, cubic ZrO2 solid solution occurs. 相似文献
19.
Hiroyasu Kido Sridhar Komarneni Rustum Roy 《Journal of the American Ceramic Society》1991,74(2):422-424
The La2 Zr2 O7 phase was prepared from metal acetylacetonates by a sol—gel route without any intermediate phase formation. X-ray peaks appeared at a temperature as low as 500°C at the positions expected for La2 Zr2 O7 , although they were broad. The crystal structure of La2 Zr2 O7 was found to be of the fluorite type below 900°C and of thepyrochlore type above 1000°C. The substitution of a small amount of Eu for La was carried out to investigate the crystal structure from the viewpoint of fluorescence, and these results confirmed the formation of fluorite type La2 Zr2 O7 below 900°C. 相似文献
20.
Riham Michelle Morcos Jean Tangeman Sergey Ushakov Alexandra Navrotsky 《Journal of the American Ceramic Society》2008,91(4):1088-1094
A series of La2 O3 –HfO2 –SiO2 glasses, approximately along the join 0.73SiO2 –0.27( x HfO2 –(1− x )La2 O3 ), 0< x <0.3), was prepared using containerless processing techniques (aerodynamic levitation combined with laser heating in oxygen). The enthalpy of formation and enthalpy of vitrification at 25°C were obtained from drop solution calorimetry of these glasses and appropriate crystalline compounds in a molten lead borate (2PbO–B2 O3 ) solvent at 702°C. The enthalpy of formation from crystalline oxides was exothermic and became less exothermic with increasing HfO2 content. Heat contents were measured by transposed temperature drop calorimetry and depended linearly on the HfO2 content. Differential scanning calorimetry showed that both the onset glass transition and the onset crystallization temperature of these glasses increased with increasing HfO2 content. Upon slow cooling in air, the glasses crystallized to a mixture of baddeleyite, cristobalite, lanthanum disilicate, and hafnon. 相似文献