Papers by Keyword: Niobates

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Authors: Hisaaki Takao, Yasuyoshi Saito, Yoshifumi Aoki, Kayo Horibuchi
Abstract: The microstructural development of crystalline-oriented (K0.5Na0.5)NbO3 (described as KNN hereafter)-based piezoelectric ceramics during sintering was investigated. The addition of CuO as a sintering aid was found to be effective for fabricating highly oriented and dense KNN ceramics. KNN specimens with 0.5-1.0 mol% CuO sintered at 1100°C for 1 h have both a relative density and a pseudo-cubic {100} orientation degree of 95% or higher. In the early stages of sintering, KNN is formed in the reaction between complementary reactants NaNbO3 and KNbO3, after which oriented grain growth proceeds at a relative density of more than 90%. In addition, the results of TEM observation showed that textured KNN ceramics have a unique pectinate-like domain structure, in which the domain walls consist of {101} planes.
Authors: Min Soo Kim, Sin Woong Kim, Soon Jong Jeong, Jae Sung Song
Abstract: Dense Li2O excess (Na0.49K0.49Li0.02)(Nb0.8Ta0.2)O3 [NKLNT] ceramics were developed by conventional sintering process without any special technique. The electrical properties of NKNLT ceramics were investigated as a function of Li2O concentration. When the sample sintered at 1050 oC for 4 h with the addition of 1 mol% Li2O, electro-mechanical coupling factor (kP) and piezoelectric coefficient (d33) were found to reach the highest values of 0.42 and 260 pC/N, respectively.
Authors: Qing Li, Li Ya Wang, Xiu Kai Li
Abstract: A nanocasting method using SBA-15 as a hard template was adopted to prepare mesoporous nanocrystalline ANbO3 (A = Li, Na, and K) samples. The characteristics of samples werecharacterized by techniques such asXRD, N2-sorption measurement, HRTEM and UVDRS. It was found that thealkality of the alkali metals could have profound impacts on the synthesis andthe physical properties of samples. The Li, Na, and K precursors can reacteasily with the siliceous template, and the reactivity varies with the alkalityof the alkali metal. The synthesis of KNbO3 is unsuccessful because of the high alkality ofK. The templated LiNbO3 andNaNbO3 consist of single crystalline nanoparticles that generate interparticle mesoporosity. The LiNbO3andNaNbO3 samples showed notably enhanced photocatalytic activitiesfor 2-propanol photodegradation in comparison to the counterparts prepared bythe solid state reaction.
Authors: S.D. Kobylianska, Oleg I. V'yunov, Anatolii G. Belous, O. Bohnke
Abstract: Solid solutions with defect perovskite structure have been obtained in the systems Li0,5-уNayLa0,5TiO3, Li0.5-yNayLa0.5◊Nb2O6 and Li0.5-yNayLa0.5◊Та2O6 at 0 ≤ y ≤ 0.5. Their structure has been shown to undergo partial disordering with increasing sodium content in the system Li0.5-yNayLa0.5◊Nb2O6 as in the system Li0.5-yNayLa0.5◊Та2O6 structure has been ordering. Lithium diffusion in system Li0,5-уNayLa0,5TiO3 follows a percolation model for the lithium diffusion. The ionic conductivity as a function of sodium content in the system Li0.5-yNayLa0.5◊Nb2O6 has a maximum. The ionic conductivity of Li0.5-yNayLa0.5◊Ta2O6 samples decreases with sodium content.
Authors: Daiki Sakuraba, Kenji Toda, Kazuyoshi Uematsu, Mineo Sato
Authors: F. Azough, Colin Leach, Robert Freer
Abstract: Ba(Me1/3Nb2/3)O3 (Me=Zn, Co, Ni and Mg) ceramics were prepared using the conventional mixed oxide route; additives included Al2O3, Ga2O3, SiO2, WO3, B2O3 and V2O5. Powders were mixed, milled for 18h, calcined at 1100°C, remilled pressed into pellets at 100 MPa, sintered in air at temperatures in the range 1350-1550°C and then cooled at 360C h–1 to 5°C h–1. Products were characterised in terms of phase analysis (X-ray diffraction), microstructure (SEM and TEM) and electrical properties (relative permittivity, εr, dielectric Q value and temperature coefficient of resonant frequency,τf). The Q values of the Ba(Me1/3Nb2/3)O3 ceramics depend on the degree of cation ordering and the additives. Slow cooling leads to 1:2 ordering of the B sites and enhanced dielectric Q values. For samples cooled at 5°C h–1 after sintering the Qxf values are in the range 28000 to 98000 GHz, and are in the sequence Ba(Ni1/3Nb2/3)O3, Ba(Co1/3Nb2/3)O3, Ba(Mg1/3Nb2/3)O3 and Ba(Zn1/3Nb2/3)O3. Additions of BaO-4WO3 or V2O5 yield higher Qxf values than Al2O3. Highly ordered Ba(Zn1/3Nb2/3)O3 has a relative permittivity of 39.4, but most other Ba(Me1/3Nb2/3)O3 ceramics exhibit εr of 31-32. The temperature coefficient of resonant frequency, τf, varies from –18 ppm/°C (Ba(Ni1/3Nb2/3)O3) to +32 ppm/°C (Ba(Mg1/3Nb2/3)O3); the sintering additives (Al2O3 and BaO-4WO3) change τf by typically 10-16 ppm/°C.
Authors: Eliane Ayumi Namikuchi, Marcos Augusto Lima Nobre, Silvania Lanfredi
Abstract: Niobates with tetragonal tungsten bronze TTB-type structure have presented great technological potential due to their dielectric, ferroelectric, pyroelectric properties. The preparation by the modified polyol method and structural characterization of K2Nd(1-x)EuxNb5O15 nanopowders, where x = 0; 0.0025; 0.025; 0.05 e 0.1, were investigated. The structural parameters were analyzed as a function of concentration of europium ions in the K2NdNb5O15 host structure using the Rietveld method. From structural parameters was determined the TTB-type structure with tetragonal symmetry, where the pentagonal sites is occupied by K+ and Eu3+ ions and tetragonal sites is occupied only by Nd3+ ions. The addition of europium in the host structure led to a decrease in the lattice parameters, compatible with the increasing degree of distortion of NbO6 polyhedra. The average crystallite size showed values between 18.25 and 26nm.
Authors: Rob C. Pullar, Chang Lai, Neil McN. Alford
Abstract: The copper-niobates, M2+Cu¬2Nb2O8 (M2+ = Zn, Co, Ni, Mg or Ca) have good microwave dielectric properties when sintered between 985 – 1010oC, and 1110oC for CaCu¬2Nb2O8. Therefore they would be potential dielectric Low Temperature Co-fired Ceramic (LTCC) materials if they could be made to sinter below 960oC (melting point of silver). To this end, additions of 3wt% V2O5 were made to ZnCu2Nb2O8, CoCu2Nb2O8, NiCu2Nb2O8, MgCu2Nb2O8 and CaCu2Nb2O8, and their sintering and dielectric behaviour was investigated for samples fired between 800 and 950oC. Doping lowered sintering temperatures to below the 960oC limit in all cases. Doping had the general effect of reducing r, density, Qf and f, although doped CaCu2Nb2O8 had a Qf value of 9300 GHz, nearly four times that of the best undoped sample. When doped and undoped samples all fired to 935oC were compared, all doped samples had greater r and density, and all except ZnCu2Nb2O8 had a smaller f.
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