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1.
B.‐J. Fang Y.‐J. Shan H.‐Q. Xu H.‐S. Luo Z.‐W. Yin 《Advanced functional materials》2004,14(2):169-173
Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 (PZNT91/9) single crystals were grown by two methods: from solution using PbO as a self‐fluxing agent (SC method) and directly from the melt without fluxing (MC method). In both growth methods, an allomeric Pb[(Mg1/3‐Nb2/3)0.69Ti0.31]O3 (PMNT69/31) single crystal was used as a seed. X‐ray diffraction patterns of ground crystals showed that phase‐pure perovskite PZNT91/9 single crystals were successfully fabricated by the above two methods. The composition of the crystals obtained by both the SC and MC methods was analyzed using X‐ray fluorescence, which confirmed that the crystal composition is close to the nominal value, although volatilization of PbO and segregation during crystal growth are inevitable. The MC PZNT91/9 crystals exhibit excellent piezoelectric properties, with the piezoelectric constant, d33, in the range of 1800–2200 pC N–1. This value is comparable to that of the SC crystals. However, the MC crystals show an abnormal dielectric behavior. In contrast with the SC crystals, in the MC crystals a much broader dielectric peak appears in the dielectric response curves, accompanied by a much lower peak temperature of around 105 °C. Furthermore, frequency dispersion is apparent over a much wider temperature range (even more apparent than in pure relaxors), where a large, i.e., about 70 °C, full width at half maximum (FWHM) for the dielectric peaks is observed in the dielectric response. It is speculated that such an unusual phenomenon correlates with defects, microinhomogeneities, and polar regions in the as‐grown MC crystals. The origins of this abnormality have not been interpreted in detail until now. However, optical observation of the domain structure confirms that both the SC and MC crystals possess complex structural states. 相似文献
2.
Control over crystallographic orientation in ceramic thin films is important for highly anisotropic structures. Layered perovskites, like Bi4 Ti3 O12 , have interesting properties associated with their ferroelectric nature, which may be fully exploited only when films are highly textured. Textured films of this titanate were fabricated via a sol–gel technique without using epitaxial growth. Orientation in the film is confirmed by XRD and SEM, and supported by refractive index and dielectric measurements. In an attempt to explain the orienting effect, light scattering experiments were conducted to yield information about the molecular size, shape, and conformation of macromolecules as the sol–gel solution ages and condensation reactions proceed. These experiments clearly show an increase in the size of molecular clusters with time. We believe that it is the organization of these large clusters during spin coating, and the relationship of the backbone chemistry to the crystal structure of Bi4 Ti3 O12 , that are responsible for the observed orientation. 相似文献
3.
Toshio Kimura Toru Takahashi Toshihiko Tani Yasuyoshi Saito 《Journal of the American Ceramic Society》2004,87(8):1424-1429
Bi0.5 Na0.5 TiO3 (BNT) and 0.94Bi0.5 Na0.5 TiO3 ·0.06BaTiO3 (BNT–BT) bulk ceramics with extensive 〈100〉 texture were prepared by the reactive-templated grain growth method, using platelike Bi4 Ti3 O12 (BIT) particles as templates for BNT. Calcined compacts were composed of matrix grains with random orientation and 〈100〉-oriented grains transformed from aligned BIT particles, and the texture developed by the growth of oriented grains during sintering. Ceramics with extensive texture were obtained by using the starting mixture containing the maximum concentration of platelike BIT to form the maximum volume fraction of oriented grains. 相似文献
4.
Effect of Acceptor and Donor Dopants on the Dielectric and Tunable Properties of Barium Strontium Titanate 总被引:1,自引:0,他引:1
Xiaofeng Liang Zhongyan Meng Wenbiao Wu 《Journal of the American Ceramic Society》2004,87(12):2218-2222
The effects of different concentrations of Mn2+ , Mg2+ , Al3+ , Fe3+ , La3+ , and Nb5+ on the dielectric and tunable properties of Ba0.6 Sr0.4 TiO3 ceramics were investigated. It was found that doping in small amounts with acceptor ions such as Mg2+ , Fe3+ , and Al3+ could meliorate the dielectric properties clearly. Decrease of dielectric loss was attributed to the formation of compensating defects originating from acceptor substitution. It was concluded that the tunability was linked to both the dielectric constant and the grain size. A higher figure of merit was obtained by doping the ceramics with smaller ions of Al and Fe, compared to Ti. 相似文献
5.
Photocatalytic activities for water decomposition were examined for photocatalysts using hexa- and octa-titanates and TiO2(B) with different tunnel space in the structure. Using RuO2 as promoter, M2Ti6O13 (M = Li, Na, K, Rb) showed the stoichiometric production of Hz and O2 except for Li, whereas H2Ti8O17 and TiO2(B) had very low activity producing only hydrogen as a product. The effects of promoters on Na2Ti6O13 showed that the activity increased in the order of RuO2 > RuO2 + IrO2 > IrO2 > RuO2 + Pt > MnO2. These effects along with other related ones are discussed: it emerges that the presence of the tunnels is important for the achievement of high photocatalytic activity. 相似文献
6.
Fred J. Parker 《Journal of the American Ceramic Society》1990,73(4):929-932
The characterization and properties of ceramic composites containing the phases Al2 TiO5 , ZrTiO4 , and ZrO2 are described. The range of compositions investigated gives very low average thermal expansions (α24–1000°C as low as −2.0 × 10−6 °C−1 ) and excellent high-temperature stability. The low thermal expansions are apparently due to a combination of microcracking by the titanate phases and a contractive phase transformation by the ZrO2 . The crystal chemistry and microstructure of the product are processing dependent. Although the composites represent a complex microcracking system, the low thermal expansions and high-temperature stability make them potential candidates for commercial applications requiring thermal shock resistance. 相似文献
7.
Hiroyuki Ikawa Hiromasa Shimojima Kazuyori Urabe Osamu Fukunaga 《Journal of the American Ceramic Society》1991,74(8):1899-1904
Axial and dilatometric thermal expansions and phase transformations were studied for solid solutions having the α-PbO2 structure in the ZrTiO4 —In2 O3 —M2 O5 (M = Sb, Ta) system with nominal formulas of Zr x Ti y In z Sb z O4 and Zr x Ti y In z Ta z O4 where x + y + 2 z = 2. With increased substitution of z , the cell volume increased, the difference in the b parameters at room temperature between those quenched from 1400° and 1000°C decreased, and the thermal expansion decreased. The axial thermal expansion of ZrTi y In z · Ta z O4 with z = 0.3 was almost identical with that of HfTiO4 , and those with z = 0.4 and z = 0.45 were smaller than that of HfTiO4 . Unit-cell volumes of these compound were compared with those of single oxides to make it clear that the unit-cell volume of ZrTiO4 was small anomalously and to distinguish the normal and abnormal substitution systems. These results were explained by the working hypothesis proposed for these compounds. 相似文献
8.
Gerhard Bayer Martin Hofmann Ludwig J. Gauckler 《Journal of the American Ceramic Society》1991,74(9):2205-2208
New oxide compounds with α-PbO2 structure have been synthesized by solid-state reactions. These are derived from ZrTiO4 and HfTiO4 by a different kind of ionic substitution. The thermal expansion behavior of these phases was investigated by means of a dilatometer and an X-ray heating diffractometer. These measurements revealed rather low expansion for some of the Zr(Me3+ /Me5+ )O4 , solid solutions. This behavior is attributed to their high expansion anisotropy, which leads to extended formation of microcracks. 相似文献
9.
The holmium substituted Ba1−3x/2HoxZr0.025Ti0.975O3 (x=0.01, 0.02, 0.025, 0.05) compositions were synthesized by the solid state reaction technique. The synthesized specimens were characterized for their structural and electrical properties using X-ray diffractometer, scanning electron microscopy, impedance analyzer and loop tracer. Phase analysis shows the formation of secondary phase Ho2Ti2O7 for Ho≥2.5 mol% substitution. The microstructural investigation shows that the holmium substitution significantly reduces the grain size. The substitution of holmium increases the Curie temperature for x≤0.02 whereas Curie temperature decreases for x≥0.025. The maximum dielectric constant at transition temperature is observed for x=0.02. The solubility limit is 2 mol% and for x≥0.025 some of the holmium atoms enter B-sites and forms the secondary phase. An increase is observed in the coercive field of the specimens with the increasing holmium content. 相似文献
10.
Murat Özen Myrjam MertensJan Luyten Frans SnijkersHans D’Hondt Pegie Cool 《Ceramics International》2012,38(1):619-625
In this paper, the amorphous barium titanate precursor was prepared by the peroxo-hydroxide method and post-treated by various drying procedures, such as: room temperature drying, room temperature vacuum drying and vacuum drying at 50 °C. The objective in the latter two treatments was to increase the Ti-O-Ba bonds of the precursor. The post-treated precursors were compared with the untreated (i.e., ‘wet’) precursor. Also, a barium titanate precursor was prepared by an alkoxide route. Afterwards, the precursors were hydrothermally treated at 200 °C in a 10 M NaOH solution. Vacuum drying of the precursor seemingly promoted the formation of Ti-O-Ti bonds in the hydrothermal end-product. The low Ba:Ti ratio (0.66) of the alkoxide-route prepared precursor lead to a multi-phase hydrothermal product with BaTiO3 as the main phase. In contrast, phase pure BaTiO3, i.e. without BaCO3 contamination, was obtained for the precursor which was dried at room temperature. Cube-shaped and highly crystalline BaTiO3 particles were observed by electron microscopy for the hydrothermally treated peroxo-hydroxide-route prepared precursor. 相似文献