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1.
Hiroaki Takeda Tomoaki Kuze Takashi Nishida Kiyoshi Uchiyama Tadashi Shiosaki 《Materials Research Bulletin》2008,43(7):1731-1736
The influences of aluminum substitution for gallium in the langasite-type La3Nb0.5Ga5.5O14 (LNG) crystals on their growth and electric properties were investigated. Al-substituted LNG (La3Nb0.5Ga5.5−xAlxO14; LNGAx) single crystals up to the solubility limit x = 0.2 have been grown by the conventional Czochralski technique. The electric properties of the LNGAx crystals were investigated and compared to those of LNG. With Al substitution, the piezoelectric constants, d11 and d14, were slightly higher. The LNGAx crystals showed a temperature dependence of d11 similar to that of the LNG crystal. 相似文献
2.
G. M. Kuzmicheva E. A. Tyunina E. N. Domoroshchina V. B. Rybakov A. B. Dubovskii 《Inorganic Materials》2005,41(4):412-419
The structure of langatate (as-grown and vacuum-annealed: LGT-I and LGT-II, respectively) and langanite (seed- and tail-end portions: LGN-III and LGN-IV, respectively) single crystals grown by the Czochralski technique from charges of nominal composition La3Ga5.5M0.5O14 = La3(Ga0.5M0.5)(1)Ga3(2)Ga2(3)O14 (M=Ta5+, Nb5+) is studied by x-ray diffraction. The LGT-I and LGT-II crystals are shown to differ in the Ga and Ta distributions over crystallographic sites: La3(Ga0.52)Ta0.48(2)
5+Ga3(Ga0.94Ta0.06(1)
3+)2O14 in LGT-I (Ta5+ in the octahedral site Ga(1) and Ta3+ in the trigonal-pyramidal site Ga(3)) and La3(Ga0.55Ta0.45(2)
5+)Ga3Ga2O13.93(2)0.07 in LGT-II (Ta5+ in the octahedral site Ga(1) and oxygen vacancies in O(1)). The increased Ta content is responsible for the lower structural perfection of LGT-I. LGN-III and LGN-IV have essentially identical compositions, La3(Ga0.47Nb0.53(1)
5+)Ga5O14 and La3(Ga0.48Nb0.52(1)
5+)Ga5O14, respectively, but differ in polarity.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 4, 2005, pp. 485–492.Original Russian Text Copyright © 2005 by Kuzmicheva, Tyunina, Domoroshchina, Rybakov, Dubovskii. 相似文献
3.
Langanite (La3Ga5.5Nb0.5O14, LGN) and its isomorphs are a few piezoelectric materials which have the unique temperature compensation and piezoelectric properties. But the high Ga2O3 content makes them very expensive and limits their applications. We reported a new langanite-type compound La3Al5.5Nb0.5O14 (LAN) which has the advantage of no Ga2O3 content. Chemically homogeneous La3Al5.5Nb0.5O14 sol was synthesized using La (NO3)3·6H2O, Al (NO3)3·9H2O and niobium citrate as starting materials. Single-phased LAN powder was prepared by decomposition of a citrate polymer precursor and subsequent reactions at high temperatures. TG-DTA, XRD and FTIR were employed to investigate the transformation process of gel to LAN powder. The results showed that, after calcination at 900 °C, pure La3Al5.5Nb0.5O14 polycrystalline powder with a narrow particle size distribution was obtained, which has the same structure with La3Ga5.5Nb0.5O14. 相似文献
4.
Hiroaki Takeda Tsuguo Fukuda Hiroyuki Kawanaka Norio Onozato 《Journal of Materials Science: Materials in Electronics》2001,12(3):199-202
The phase diagram of the La2O3-Ta2 O5-Ga2 O3 system around La3 Ta0.5 Ga5.5 O14 (LTG) was investigated by a differential thermal analysis and the quenching method. La3 Ta0.5 Ga5.5 O14 single crystals were subsequently grown from different starting melt compositions using the Czochralski technique. The effect of the starting melt composition on crystal quality was examined by measuring the variation in the chemical composition and lattice parameters along the growth axis. On the basis of these experimental results, we have grown LTG single crystals over 2 inches in diameter. 相似文献
5.
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
6.
D. Arumugam 《Materials Research Bulletin》2010,45(12):1825-1831
LiMn2O4 spinel cathode materials were coated with 1.0, 2.0 and 3.0 wt.% of La2O3 by polymeric process, followed by calcinations at 850 °C for 6 h in air. The surface coated LiMn2O4 cathode materials were physically characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and XPS. XRD patterns of La2O3-coated LiMn2O4 revealed that the coating did not affect the crystal structure and space group Fd3m of the cathode materials, compared to the uncoated LiMn2O4. The surface morphology and particle agglomeration were investigated using scanning electron microscopy and the TEM image showed a compact coating layer on the surface of the core materials that had average thickness of about 100 nm. XPS data illustrated that the La2O3 was completely coated over the surface of the LiMn2O4 core cathode materials. The galvanostatic charge and discharge of the uncoated and La2O3-coated LiMn2O4 cathode materials were carried out in the potential range of 3.0 and 4.5 V at 30 °C and 60 °C. Among them, 2.0 wt.% of La2O3-coated spinel LiMn2O4 cathode has improved the structural stability, high reversible capacity and excellent electrochemical performances of the rechargeable lithium batteries. 相似文献
7.
Hong Lv Bin-Yuan Zhao Yu-Ji Wu Gang Sun Gang Chen Ke-Ao Hu 《Materials Research Bulletin》2007,42(12):1999-2012
The crystal structure, thermal expansion rate, electrical conductivity and electrochemical performance of Sm0.5Sr0.5MxCo1−xO3−δ (M = Fe, Mn) have been investigated. Two crystal structures have been observed in the specimens of Sm0.5Sr0.5FexCo1−xO3−δ (SSFC) at room temperature, the perovskite structure of SSFC has an orthorhombic symmetry for 0 ≤ x ≤ 0.4 and a cubic symmetry for 0.5 ≤ x ≤ 0.9. The specimens of Sm0.5Sr0.5MnxCo1−xO3−δ (SSMC) crystallize in an orthorhombic structure. The adjustment of thermal expansion rate to electrolyte, which is one of the main problems of SSC, can be achieved to lower TEC values with more Fe and Mn substitution. Especially, Sm0.5Sr0.5Mn0.8Co0.2O3−δ exhibits good thermal compatibility with La0.8Sr0.2Ga0.8Mg0.2O3. High electrical conductivities are obtained for all the specimens and they demonstrate above 100 S/cm at 800 °C in SSFC system. The polarization resistance increases with increasing Mn content, Nevertheless, the polarization resistance of SSFC increases with increasing Fe content, but when the amount of Fe reaches to 0.4, the maximum is obtained while the resistance will decrease when the amount of Fe reaches above 0.4. Sm0.5Sr0.5Fe0.8Co0.2O3−δ electrode exhibits high catalytic activity for oxygen reduction operating at temperature from 700 to 800 °C. 相似文献
8.
Alok Kumar Rai Nitish Kumar Singh Susant Kumar Acharya Laxman Singh K.D. Mandal 《Materials Science and Engineering: B》2012,177(14):1213-1218
Tantalum (Ta5+) doped CaCu3Ti4−xTaxO12 (x = 0.05 and 0.10) ceramics were prepared by semi-wet route using solid Ta2O5 powder and metal nitrate solutions. Powder X-ray diffraction confirmed the major phase formation of cubic CaCu3Ti4O12 ceramic in the doped samples sintered at 900 °C for 6 h. Microstructure has been studied using field-emission scanning electron microscopy. The grain size is in the range of 150 nm to 1 μm for both compositions. Dielectric constant of the samples increases with increasing tantalum concentrations. 相似文献
9.
We describe the synthesis and characterization of new intergrowth Aurivillius related phases, Bi4LnNb3O15 (Ln = La, Pr, Nd) and Bi4LaTa3O15. Both powder X-ray diffraction and electron microscopy investigations show that the compounds adopt orthorhombic structures with the cell parameters a ∼ 5.5 Å, b ∼ 5.5 Å and c ∼ 20.9 Å, suggesting an ordered intergrowth structure that consists of n = 1 [Bi2NbO6]− and n = 2 [Bi2LnNb2O9]+ Aurivillius fragments which are stacked alternately along the c-axis. The oxides do not show a second harmonic generation (SHG) response toward 1064 nm laser radiation; they do not show a ferroelectric-paraelectric transition either between 30 and 900 °C in dielectric measurements, indicating a centrosymmetric structure. Optical absorption studies show that the intergrowth phases possess considerably smaller band gaps than the parent Nb2O5 and Ta2O5. 相似文献
10.
Hongmei Ren 《Materials Research Bulletin》2010,45(11):1608-1613
Na0.5Bi0.5Cu3Ti4O12 (NBCTO) ceramics were prepared by conventional solid-state reaction method. The phase structure, microstructure and dielectric properties of NBCTO ceramics sintered at various temperatures with different soaking time were investigated. Pure NBCTO phase could be obtained with increasing the temperature and prolonging the soaking time. High dielectric permittivity (13,495) and low dielectric loss (0.031) could be obtained when the ceramics were sintered at 1000 °C for 7.5 h. The ceramics sintered at 1000 °C for 7.5 h also showed good temperature stability (−4.00 to −0.69%) over a large temperature range from −50 to 150 °C. Complex impedances results revealed that the grain was semiconducting and the grain boundaries was insulating. The grain resistance (Rg) was 12.10 Ω cm and the grain boundary resistance (Rgb) was 2.009 × 105 Ω cm when the ceramics were sintered at 1000 °C for 7.5 h. 相似文献
11.
The microstructure of a perovskite, La2MnGaO6, was studied by Transmission Electron Microscopy (TEM). An idiomorphic grain exhibited a domain structure at ambient temperature, and each domain possessed a common b-axis and axial relation, [1 0 0]//[0 0 1]. When the grain was heated by a convergent electron beam, the domains vanished after the orthorhombic to rhombohedral phase transformation taking place at 423 K. The domains reappeared when cooled, although domain boundaries moved and the domains rotated by 90° with respect to the b-axis. 相似文献
12.
Lanthanum acetylacetonate La(C5H7O2)3·xH2O has been used in the preparation of the precursor solution for the deposition of polycrystalline La2O3 thin films on Si(1 1 1) single crystalline substrates. The precursor chemistry of the as-prepared coating solution, precursor powder and precursor single crystal have been investigated by Fourier Transformed Infrared Spectroscopy (FTIR), differential thermal analysis coupled with quadrupole mass spectrometry (TG-DTA-QMS) and X-ray diffraction. The FTIR and X-ray diffraction analyses have revealed the complex nature of the coating solution due to the formation of a lanthanum propionate complex. The La2O3 thin films deposited by spin coating on Si(1 1 1) substrate exhibit good morphological and structural properties. The films heat treated at 800 °C crystallize in a hexagonal phase with the lattice parameters a = 3,89 Å and c = 6.33 Å, while at 900 °C the films contain both the hexagonal and cubic La2O3 phase. 相似文献
13.
To obtain yttrium-gallium garnet (Y3Ga5O12, YGG) a simple “chimie douce” method has been developed. This sol-gel method yielded excellent starting gel precursor for the fabrication of YGG phase, which could be used as host material for optical applications. The pattern of X-ray diffraction analysis of the ceramic sample sintered for 10 h at 1000 °C showed the formation of monophasic Y3Ga5O12 phase. The phase transformations, composition and micro-structural features in the gels and polycrystalline sample were studied by thermoanalytical methods (TGA/DTA), powder X-ray diffraction analysis (XRD), infrared spectroscopy (IR) and scanning electron microscopy (SEM). The quality of the resulting products (homogeneity, crystallisation temperature, grain size, grain size distribution, etc.) is discussed. 相似文献
14.
La modified SBT (Sr0.8La0.1Bi2.1Ta2O9) thin films of different thickness were fabricated on Pt/Ti/SiO2/Si substrates by the metalorganic decomposition technique. All the films were annealed layer-by-layer at 800 °C using a rapid thermal annealing furnace. X-ray diffraction analysis indicated that the relative intensity of the (2 0 0) diffraction peak [I(2 0 0)/I(1 1 5)] increased with the increase of the film thickness. Eventually, an a-axis preferentially oriented SLBT film was obtained. These results are discussed with respect to the anisotropy of the grain growth. The a-axis preferentially oriented SLBT film, whose relative intensity of the (2 0 0) peak [I(2 0 0)/I(1 1 5)] was 1.05, had a remanent polarization (2Pr) value of 21 μC/cm2 and a coercive field (2Ec) value of 70 kV/cm under the electric field of 200 kV/cm. 相似文献
15.
Ramaswamy Murugan Werner Weppner Peter Schmid-Beurmann 《Materials Research Bulletin》2008,43(10):2579-2591
Oxides with the nominal chemical compositions Li5La3Sb2O12 and Li6SrLa2Sb2O12 were prepared by solid-state reaction. The structures were refined by the Rietveld method using powder X-ray diffraction data. The synthesis of Li5La3Sb2O12 resulted in the well known garnet-related structure plus 5 wt.% of La2LiSbO6 in the bulk. In contrast to that, Li6SrLa2Sb2O12 could be synthesised in single garnet-related type phase. Lithium ion conductivities of Li5La3Sb2O12 and Li6SrLa2Sb2O12 were studied by the ac impedance method. The grain-boundary contribution to the total (bulk + grain-boundary) resistance is very small and about 5 and 3% for Li5La3Sb2O12 and Li6SrLa2Sb2O12, respectively, at 24 °C and decreases further with increase in temperature. Among the investigated compounds, Li5La3Sb2O12 exhibits the highest total (bulk + grain-boundary) and bulk ionic conductivity of 7.8 × 10−6 and 8.2 × 10−6 S cm−1, respectively, at 24 °C. The structural data indicate that the coupled substitution Li + Sr ⇒ La leads to a closure of the bottle neck like O-O distances of the shared edges of neighbouring Li octahedra and therefore reduces the mobility of Li ions in Li6SrLa2Sb2O12. Scanning electron microscope (SEM) images of the Li6SrLa2Sb2O12 compound revealed well crystallised large homogeneous grains (∼4.8 μm) and the grains were in good contact with the neighbouring grain, which leads to a smaller grain-boundary contribution to the total resistance. 相似文献
16.
(1 − x) (K0.44Na0.52Li0.04)(Nb0.84Ta0.1Sb0.06)O3 − x BiFeO3 (x = 0, 0.002, 0.004, 0.006, 0.008, 0.01) lead-free piezoelectric ceramics were prepared by the conventional ceramic processing. The compositional dependence of the phase structure and the electrical properties of the ceramics were studied. A morphotropic phase boundary between the orthorhombic and tetragonal phases was identified in the composition range of 0.004 < x < 0.006. The ceramics near the morphotropic phase boundary exhibit a strong compositional dependence and enhanced piezoelectric properties. The ceramics with 0.6 mol.% BiFeO3 exhibit good electrical properties (d33 ∼ 246 pC/N, kp ∼ 43%, Tc ∼ 285 °C, ?r ∼ 1871, and tan δ ∼ 1.96%). These results show that the (1 − x) (K0.44Na0.52Li0.04)(Nb0.84Ta0.1Sb0.06)O3 − x BiFeO3 ceramic is a promising lead-free piezoelectric material for applications in different devices. 相似文献
17.
Ming Yang Xianli Huang Shicheng Yan Zhaosheng Li Tao Yu Zhigang Zou 《Materials Chemistry and Physics》2010
Na1−xLaxTa1−xCrxO3 and NaTa1−xCrxO3 (x = 0.01, 0.03, 0.05 and 0.10) have been synthesized by a solid state reaction method. These photocatalysts can produce H2 in the presence of methanol under visible light irradiation (λ > 420 nm). The photocatalytic activities of Na1−xLaxTa1−xCrxO3 are much higher than those of NaTa1−xCrxO3, respectively. Especially, the H2 evolution rate of Na0.9La0.1Ta0.9Cr0.1O3 is 2.2 μmol h−1, which is nearly 4 times higher than that of NaTa0.9Cr0.1O3 (0.6 μmol h−1). The improved activities of Na1−xLaxTa1−xCrxO3 compared with NaTa1−xCrxO3 can be ascribed to two factors: one is smaller particle size and higher specific surface area which is caused by the doping of lanthanum; the other is that Na1−xLaxTa1−xCrxO3 has less Cr6+, which is induced by codoping of lanthanum and chromium. 相似文献
18.
Lead borate and lead silicate were added to lower the sintering temperature of a Ni0.5Zn0.5Fe2O4 ferrite prepared from the blend of two types of powders and to homogenize the grain size. 5PbO·SiO2 and 5PbO·B2O3 flux systems were added to lower the sintering temperature and diminish the magnetic loss at high frequencies. The ferrites were studied by bulk density, scanning electron microscopy and impedance analysis. It was found that the addition of PbO markedly accelerated the grain growth, while SiO2 and B2O3 were found to be effective to obstruct the movement of grain boundaries and to minimize the grain size. Doping with PbO in the mixed powders appropriately increased the densification and initial permeability. The ferrite doped with 1% of 5PbO·SiO2 possessed the lowest loss tangent (tgδ) in the range of 5 M-40 MHz and the highest threshold frequency. 相似文献
19.
利用Mindlin板理论分析了硅酸镓镧晶体板强耦合的厚度剪切振动和弯曲振动,获得了硅酸镓镧晶体板高频振动的色散关系、频谱关系和振动模态位移图。数值计算结果表明,Mindlin板理论可以获得硅酸镓镧晶体板厚度剪切振动的一阶精确截止频率,无需修正系数。基于石英晶体谐振器设计晶片最佳长厚比的选取方法,确定了硅酸镓镧晶片的最佳尺寸,避免了厚度剪切振动模态和弯曲振动模态的强耦合。通过绘制硅酸镓镧晶体板在最佳尺寸时的各振动模态位移图,发现厚度剪切振动模态是主振模态,具有很好的能陷效应。Mindlin板理论在硅酸镓镧晶体板高频振动的应用分析可以指导硅酸镓镧晶体谐振器的实际研发。 相似文献
20.
Single crystal of a novel compound, K1.83Ba4.17Nb12.18O36, has been synthesized in the course of investigation on the K2O-BaO-Nb2O5 system. The crystal structure was determined by single crystal X-ray diffraction data. The space group of this compound was found to be P6/mmm (#191) with the lattice parameters of a = 21.109(4) and c = 3.967(1) Å. The final R-factors were R = 0.039 and Rw=0.042 for unique 508 reflections. The crystal structure had the same tunnel structure as that of hexagonal BaTa2O6 (H-BaTa2O6), which is the high temperature form in three modifications of BaTa2O6. The chemical composition of K1.83Ba4.17Nb12.18O36 was close to that of the tetragonal tungsten bronze (TTB) type KBa2Nb5O15 and the powder samples within this composition were prepared so as to clarify the boundary between H-BaTa2O6 and TTB-type structures. The H-BaTa2O6-type structure appears in (K + Ba)/Nb ≤ 0.500 and the TTB-type structure is in (K + Ba)/Nb ≥ 0.575. The dielectric constants of these samples were measured from room temperature to 500 °C for sintered body. The TTB-type compounds exhibited ferroelectric temperature dependence with the Curie points of 284-372 °C and the H-BaTa2O6-type compounds were not ferroelectrics as predicted from the crystal structure analysis. 相似文献