共查询到20条相似文献,搜索用时 15 毫秒
1.
M ThirumalI.N Jawahar K.P SurendiranP Mohanan A.K Ganguli 《Materials Research Bulletin》2002,37(14):2321-2334
Oxides belonging to the families Ba3ZnTa2−xNbxO9 and Ba3MgTa2−xNbxO9 were synthesized by the solid state reaction route. Sintering temperatures of 1300°C led to oxides with disordered (cubic) perovskite structure. However, on sintering at 1425°C hexagonally ordered structures were obtained for Ba3MgTa2−xNbxO9 over the entire range (0≤x≤1) of composition, while for Ba3ZnTa2−xNbxO9 the ordered structure exists in a limited range (0≤x≤0.5). The dielectric constant is close to 30 for the Ba3ZnTa2−xNbxO9 family of oxides while the Mg analogues have lower dielectric constant of ∼18 in the range 50 Hz to 500 kHz. At microwave frequencies (5-7 GHz) dielectric constant increases with increase in niobium concentration (22-26) for Ba3ZnTa2−xNbxO9; for Ba3MgTa2−xNbxO9 it varies between 12 and 14. The “Zn” compounds have much higher quality factors and lower temperature coefficient of resonant frequency compared to the “Mg” analogues. 相似文献
2.
Teruki Motohashi Yohei Hamade Takashi Takeda Kei-ichiro Murai Shinich Kikkawa 《Materials Research Bulletin》2009,44(9):1899-5948
Pure Ca1−xEuxTa(O,N)3 were successfully synthesized in the whole range of Ca/Eu compositions by means of ammonia nitridation via a citrate precursor route. As-nitrided products with x < 0.4 were apparently orthorhombic, while those with x ≥ 0.4 crystallized in a cubic structure. The anionic composition was found to be essentially O2N and independent of Eu content (x). The as-nitrided EuTaO2N possessed a cubic perovskite-type structure, while high-temperature post-annealing led to a tetragonal EuTaO2N phase with better crystallinity. The re-nitridation transformed the post-annealed product into the original cubic lattice, which might be an average of the tetragonal micro-domains. 相似文献
3.
Wangchang Geng Xiaotian Li Xiaoyong Lai Beihong Long Jinchun Tu 《Materials Research Bulletin》2008,43(3):601-610
(MgO)x(ZnO)1−x materials have been synthesized using mesoporous carbon as template. By increasing the MgO content in the materials greater than 25%, the (MgO)x(ZnO)1−x materials began to form the mesoporous structure. Pore size distribution curves indicated that the BJH pore diameter decreased with increasing MgO content. In photoluminescence spectra, all the samples except pure ZnO showed both the band-edge emission and the deep-level emission (green band). It was interesting to note that the UV emission peak energy (EUV) had a red-shift of about 48 meV at the low MgO content range of 0-25%, while when the MgO content varied from 25 to 75%, the EUV displayed a blue-shift of about 36 meV to the higher energy direction. The optical band gap (Eg) of the (MgO)x(ZnO)1−x calculated from the absorption spectra was far smaller than that in literature, and this may be related to the formation of mesoporous structure. 相似文献
4.
The crystal structures of two PbSb2O6-type compounds containing titanium, CdTi2O4(OH)2 and LaTiSbO6 were refined by X-ray powder diffraction data. For both compounds structure refinements with the space group were successful and the R-factors were RWP = 6.46% and RP = 4.90% for CdTi2O4(OH)2 and RWP = 9.55% and RP = 7.17% for LaTiSbO6. These crystal structures were the same as that of the typical PbSb2O6-type compound in spite of the existence of protons in the interlayer or two different metal ions in the layer. 相似文献
5.
The effects of B2O3 addition on the microwave dielectric properties and the microstructures of (1−x)LaAlO3-xSrTiO3 ceramics prepared by conventional solid-state routes have been investigated. Doping with 0.25 wt.% B2O3 can effectively promote the densification and the microwave dielectric properties of (1−x)LaAlO3-xSrTiO3 ceramics. It is found that LaAlO3-SrTiO3 ceramics can be sintered at 1400°C due to the liquid phase effect of a B2O3 addition observed by scanning electronic microscopy (SEM). The dielectric constant as well as the Q×f value decreases with increasing B2O3 content. At 1460°C, 0.46LaAlO3-0.54SrTiO3 ceramics with 0.25 wt.% B2O3 addition possesses a dielectric constant (εr) of 35, a Q×f value of 38,000 (at 7 GHz) and a temperature coefficients of resonant frequency (τf) of −1 ppm/°C. 相似文献
6.
Theeranun Siritanon 《Materials Research Bulletin》2011,46(12):2494-2496
CsTe2O6 adopts a rhombohedrally distorted pyrochlore related structure due to the 1:3 ordering of Te4+ and Te6+ in the octahedral sites respectively. Phases of the type CsTe2−xWxO6 were found to have the cubic pyrochlore structure from x = 0.2 to 0.5. These phases all contain Te4+ and Te6+ (mixed with W6+) and are disordered in octahedral sites of the pyrochlore structure. This mixed valence situation results in strong optical absorption in the visible region of the spectrum but does not produce a measurable electrical conductivity. 相似文献
7.
The structure, ferroelectric characteristics and piezoelectric properties of (Na0.5Bi0.5)1 − xBaxTiO3 (x = 0.04, 0.06, 0.10) ceramics prepared by conventional solid state method were investigated. The influences of poling condition and sintering temperature on the piezoelectric properties of the ceramics were examined. The piezoelectric properties of the ceramics highly depend on poling field and temperature, while no remarkable effect of poling time on the piezoelectric properties was found in the range of 5-25 min. Compared with (Na0.5Bi0.5)0.96Ba0.04TiO3 and (Na0.5Bi0.5)0.90Ba0.10TiO3, the piezoelectric properties of (Na0.5Bi0.5)0.94Ba0.06TiO3 are more sensitive to poling temperature due to the relatively low depolarization temperature. Moderate increase of sintering temperature improved the poling process and piezoelectric properties due to the development of microstructural densification and crystal structure. With respect to sintering behavior and piezoelectric properties, a sintering temperature range of 1130-1160 °C was ascertained for (Na0.5Bi0.5)0.90Ba0.10TiO3. 相似文献
8.
Takeshi Oishi 《Materials Research Bulletin》2007,42(12):2072-2081
The crystal structure and microwave dielectric properties of the (Sm1−xYx)(Ti1.5W0.5)O6 (x = 0 and 0.5) ceramics sintered at 1375 °C for 2-50 h were investigated in this study. No secondary phase was observed in the samples sintered for various sintering times, whereas a secondary phase was formed in the (Sm0.5Y0.5)(Ti1.5W0.5)O6 ceramic sintered at 1400 °C for 50 h. As for the microstructure analysis, the formation of the liquid phase was observed in the both of the samples sintered for 20 and 50 h. The formation of the liquid phase is related to the compositional change of Ti and W from the stoichiometric composition of the samples caused by the instability of crystal structure. The dielectric constants were increased with increased sintering time in the both of the samples, though variations in the temperature coefficient of resonant frequency of the samples were not recognized with the variation in the sintering time. Moreover, although the quality factors of the each sample increased with increasing the sintering time from 2 to 10 h, decreases in the quality factors were recognized when the sintering time was over 10 h. 相似文献
9.
Ba1−ySryLa4−xTbx(WO4)7 (x = 0.02-1.2, y = 0-0.4) phosphors were prepared via a solid-state reaction and their photoluminescence properties were investigated. An analysis of the decay behavior indicates that the energy migration between Tb3+ ions is conspicuous in the 5D3 → 7F4 transition due to the cross-relaxation in BaLa4(WO4)7. A partial substitution of Ba2+ by Sr2+ can not only enhance the emission intensity but also increase the solid solubility of Tb3+ in Ba1−ySryLa4−xTbx(WO4)7. The emission intensity of the 5D4 → 7FJ (J = 4, 5, 6) transitions can be enhanced by increasing Sr2+ and Tb3+ concentrations, with the optimal conditions being x = 1.2, y = 0.4 (Ba0.6Sr0.4La2.8Tb1.2(WO4)7). Under near-UV excitation at 379 nm, the CIE color coordinates of Ba1−ySryLa4−xTbx(WO4)7 vary from blue (0.212, 0.181) at x = 0.04, y = 0, to green (0.245, 0.607) at x = 1.2, y = 0.4. 相似文献
10.
Zirconium titanate-stannate doped with V with co-dopants Al, In or Y was synthesised by solid state reaction and its structural (XRD, SEM), optical (DRS) and technological properties were determined to assess its potential use as ceramic pigment. These compounds have a srilankite-type, disordered orthorhombic structure, implying a random distribution of Zr, Ti, Sn and dopants in a single, strongly distorted octahedral site. Doping caused an increase of unit-cell dimensions, metal-oxygen distances and octahedron distortion. Optical spectra show crystal field electronic transitions of V4+ as well as intense bands in the blue-UV range due to V4+-V5+ intervalence charge transfer and/or to V-O charge transfer. The formation of oxygen vacancies is supposed to compensate the occurrence of V4+ ensuring the lattice charge neutrality. These srilankite-type oxides develop a deep and brilliant yellow shade with colourimetric parameters close to those of industrial ceramic pigments. Technological tests in several ceramic applications proved that zirconium titanate-stannate is very stable at high temperature, exhibiting an excellent performance in the 1200-1250 °C range, even better than praseodymium-doped zircon. 相似文献
11.
Microstructure and microwave dielectric characteristics of (1 − x)Ba(Zn1/3Ta2/3)O3-xBaTi4O9 ceramics
Wen-Cheng Tzou Yao-Sheng Yang Ho-Hua Chung Chien-Chen Diao 《Materials Research Bulletin》2007,42(11):1897-1904
(1 − x)Ba(Zn1/3Ta2/3)O3-xBaTi4O9 (0.1 ≤ x ≤ 0.85) composites are prepared by mixing 1150 °C-calcined BaTi4O9 with 1150 °C-calcined Ba(Zn1/3Ta2/3)O3 powders. The crystal structure, microwave dielectric properties and sinterabilites of the (1 − x)Ba(Zn1/3Ta2/3)O3-xBaTi4O9 ceramics have been investigated. X-ray diffraction patterns reveal that BaTi4O9, ordered and disordered Ba(Zn1/3Ta2/3)O3 phases exist independently over the whole compositional range. The sintering temperatures of (1 − x)Ba(Zn1/3Ta2/3)O3-xBaTi4O9 ceramics are about 1240 - 1320 °C and obviously lower than those of Ba(Zn1/3Ta2/3)O3 ceramics. The dielectric constants (?r) and the temperature coefficient of resonant frequency (τf) of (1 − x)Ba(Zn1/3Ta2/3)O3-xBaTi4O9 ceramics increase with the increase of BaTi4O9 content. Nevertheless, the bulk densities and the quality values (Q × f) of (1 − x)Ba(Zn1/3Ta2/3)O3-xBaTi4O9 ceramics increase with the increase of Ba(Zn1/3Ta2/3)O3 content. The results are attributed to the higher density and quality value of Ba(Zn1/3Ta2/3)O3 ceramics, the better grain growth, and the densification of sintered specimens added a small BaTi4O9 content. The (1 − x)Ba(Zn1/3Ta2/3)O3-xBaTi4O9 ceramic with x = 0.1 sintered at 1320 °C exhibits a ?r value of 31.5, a maximum Q × f value of 68500 GHz and a minimum τf value of 4.1 ppm/°C. 相似文献
12.
La2−xBaxMo2O9−x/2 (x ≤ 0.18) have been prepared by solid state reaction method. The lattice parameter of La2−xBaxMo2O9−x/2 (x ≤ 0.18) determined by XRD data refinement shows a linear dependence on the dopant Ba content x. For the specimen with a La/Ba molar ratio of 0.18-0.2, additional reflection of secondary phase exists in the XRD pattern, so the value of solubility limit for Ba in La2Mo2O9 is defined in range of 0.18 < x < 0.2. As the replacement degree of La3+ by Ba2+ increases, the bulk conductivity of La2−xBaxMo2O9−x/2 (x ≤ 0.18) decreases initially and then increases, a minimum value at La1.9Ba0.1Mo2O8.95 exists. Hebb-Wagner studies in argon atmosphere, which use an oxide-ion blocking electrode, show that La2−xBaxMo2O9−x/2 (x ≤ 0.18) are predominantly oxide-ion conducting in the temperature ranging from 773 to 1173 K. The average thermal expansion coefficient of La1.84Ba0.16Mo2O8.92 determined by high-temperature XRD was deduced as great as 17.5 × 10−6 K−1 between 298 and 1173 K. 相似文献
13.
Theeranun Siritanon 《Materials Research Bulletin》2011,46(6):820-5754
Single crystals of CsMxTe2−xO6 pyrochlores with M = Al, Ga, Ge, and In have been grown from a TeO2 flux. Structure refinements from single crystal X-ray diffraction data are reported. These results are used to discuss deviations from ideal stoichiometry that result in electronic conductivity presumably related to mixed valency of tellurium. 相似文献
14.
The present work reports the effects caused by barium on phase formation, morphology and sintering of lead magnesium niobate-lead titanate (PMN-50PT). Ab initio study of 0.5Pb(Mg1/3Nb2/3)O3-0.5(BaxPb(1−x)TiO3) ceramic powders, with x = 0, 0.20, and 0.40 was proposed, considering that the partial substitution of lead by barium can reestablish the equilibrium of monoclinic-tetragonal phases in the system. It was verified that even for 40 mol% of barium, it was possible to obtain pyrochlore-free PMN-PT powders. The increase of the lattice parameters of PMN-PT doped-powders confirmed dopant incorporation into the perovskite phase. The presence of barium improved the reactivity of the powders, with an average particle size of 120 nm for 40 mol% of barium against 167 nm for the pure sample. Although high barium content (40 mol%) was deleterious for a dense ceramic, contents up to 20 mol% allowed 95% density when sintered at 1100 °C for 4 h. 相似文献
15.
Mohammed Kars Daniel C. Fredrickson Sven Lidin L.C. Otero-Diáz 《Materials Research Bulletin》2010,45(8):982-988
In the Sb-Nb-S-Se system, a new misfit layer compound (MSL) has been synthesized and its structure was determined by combining single crystal X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. It presents a composite crystal structure formed by (SbS1−xSex) slabs stacking alternately with double NbS2 layers and both can be treated as separate monoclinic subsystems. The (SbS1−xSex) slabs comprise a distorted, two-atom-thick layer with NaCl-type structure formed by an array of {SbX5} square pyramids joined by edges (X: S, Se); the NbS2 layers consist of {NbS6} trigonal prisms linked through edge-sharing to form sheets, just as in the 2H-NbS2 structure type. Both sublattices have the same lattice parameters a = 5.7672(19) Å, c = 17.618(6) Å and β = 96.18(3)°, with incommensurability occurring along the b direction: b1 = 3.3442(13) Å for the NbS2 subsystem and b2 = 2.8755(13) Å for the (SbS1−xSex) subsystem. The occurrence of diffuse scattering intensity streaked along c* indicates that the (SbS1−xSex) subsystem is subjected to extended defects along the stacking direction. 相似文献
16.
The anion-excess ordered fluorite-related phase Ba2.1Bi0.9(O, F)6.8−δ has been synthesized by a solid state reaction of BaF2, BiF3 and Bi2O3 at 873 K with subsequent short annealing at 573 K. The crystal structure of the new phase has been solved using electron diffraction and X-ray powder diffraction (a = 9.5372(1) Å, c = 18.1623(3) Å, space group I4/m, RI = 0.025, RP = 0.029). Interstitial anions in the fluorite-based structure are considered to form isolated cuboctahedral 8:12:0 clusters. The structural relationship between the oxyfluoride phase Ba2.1Bi0.9(O, F)6.8−δ and similar rare-earth-based fluorides is discussed. 相似文献
17.
B. Muktha 《Materials Research Bulletin》2007,42(12):2150-2155
A new series of solid solutions of the type, AxBa1−xBi2Mo4O16 (A = Ca, Sr, Pb) have been isolated. The domain of the solid solutions is very narrow and is in the range (0.01 ≤ x ≤ 0.10). All the phases were synthesized by the solid-state technique. The crystal structure is similar to that of the monoclinic scheelite type BaBi2Mo4O16. The structure consists of layers of [Bi2O2] units separated by (Ba/AO)10 units and isolated MoO4 tetrahedra. Their semiconductor band gaps render them as potential materials for photocatalysis. 相似文献
18.
The pseudo-binary TiO2-FeSbO4 system was investigated by means of thermogravimetric analysis below 1673 K in O2. Rutile-type solid solutions were synthesised at 1373 K in O2 by means of a solid state reaction between the two pure end members TiO2 (rutile) and FeSbO4 mixed in stoichiometric amounts. Thermal stability of the (Ti2xFe1−xSb1−x)O4 solid solution increases with rutile content; equimolar (Ti1.00Fe0.50Sb0.50)O4 solid solutions decompose at about 1673 K forming a TiO2-enriched solid solution and FeSbO4, that subsequently decomposes into Fe2O3 (hematite) and a volatile Sb oxide, probably Sb4O6. For compositions characterised by higher Ti content the decomposition temperature is higher than 1673 K. 相似文献
19.
Thermal and reduction-oxidation stability of substituted LaMn1−yCoyO3 perovskite-type oxides (0.0 ≤ yCo ≤ 1.0) prepared by the citrate route have been studied by means of surface area, X-ray diffraction, FTIR spectroscopy and magnetic properties. The perovskite orthorhombic structure is found for yCo ≤ 0.5, with the exception of yCo = 0.1, which corresponds better to rhombohedral LaMnO3.15. For yCo > 0.5 the diffraction profiles are quite similar to the cobaltite’s rhombohedral structure. Magnetic iso-field studies (ZFC-FC) reveal that, for yCo ≤ 0.50, the system presents an antiferromagnetic canted-like ordering of the Mn/Co sublattice, in which the presence of divalent Co ion creates Mn3+-Mn4+ pairs that interact ferromagnetically through the oxygen orbital. This interpretation is confirmed by the magnetization loops, in which the magnetic moment increases when substituting Mn for Co. Therefore, the general trend is: for yCo ≤ 0.5, the Co ions are inserted in the manganite structure and for yCo > 0.5, the Mn ions are inserted in cobaltite structure. The enhancement of the ferromagnetic properties and the thermal stability against reduction for yCo = 0.5 is attributed to optimized Co2+-Mn4+ interactions. 相似文献
20.
Akinori Kan Hirotaka OgawaKenkichi Mori Junji Sugishita 《Materials Research Bulletin》2002,37(8):1509-1518
The synthesis and microwave dielectric characterization of (Nd2−xLax)BaZnO5 solid solutions were studied. The samples obtained were single phase over the whole composition range and the lattice parameters of solid solutions were linearly increased with increasing the composition. Moreover, the expansion of the volume in the RO8 (R=Nd and La) and BaO10 polyhedra and ZnO4 tetrahedron were recognized when Nd ions were substituted by La. These variations in the lattice parameters and volumes of the polyhedra are basically attributed to the differences in ionic radii between Nd3+ and La3+ ions. From the evaluation of microwave dielectric properties, it was shown that the appropriate τf values ranging from 4.6 to −5.0 ppm/°C are obtained by La substitution for Nd ion, and the highest Q · f value was 17,832 GHz at x=2. 相似文献