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1.
Teiichi Hanada Yoshinari Kato Setsuhisa Tanabe Naohiro Soga 《Journal of the American Ceramic Society》1992,75(9):2335-2338
Amorphous films in the system AlPO4 –TiO2 were prepared by an rf-sputtering method, and their physical properties, such as density, refractive index, and thermal expansion coefficient, and the infrared absorption spectra were measured. The thermal expansion coefficient increased linearly with increasing TiO2 content. The results of the molar refractivity and the infrared absorption spectra indicated that the coordination number of titanium ions in these films is higher than that in SiO2 –TiO2 glasses with a negative thermal expansion, in which Ti4+ ions are tetrahedrally coordinated. In order to confirm the coordination state of the titanium ions in these amorphous films, titanium K -band emission spectra were obtained by X-ray emission spectroscopy, revealing sixfold coordination. The higher coordination state of Ti4+ was considered to account for these amorphous films not exhibiting negative thermal expansion, as in the SiO2 –TiO2 system. 相似文献
2.
Compatibility relations of Al2 03 in the quaternary system Zr02-Al2 03 -Si02 -CaO were studied by firing and quenching followed by microscopy and energy-dispersive X-ray examination. A projection of the boundary surface of the primary crystallization volume of Al2 03 was constructed in terms of the CaO, Si02 , and Zr02 contents of the mixtures recalculated to 100 wt%. Two invariant points, where four solids coexist with a liquid phase, are defined, and the positions of the isotherms were established. 相似文献
3.
Kentaro Fukuda Teiichi Hanada Setsuhisa Tanabe Takeshi Yao 《Journal of the American Ceramic Society》2002,85(4):915-920
Amorphous films in the system Al2 O3 –Y2 O3 were prepared by the rf sputtering method in the range of 0–76 mol% Y2 O3 , and their density, refractive index, and elastic constants were measured. All of the physical properties of the amorphous Al2 O3 –Y2 O3 films had a similar compositional dependence; that is, they increased continuously, but not linearly with increasing Y2 O3 content. To confirm the coordination states of aluminum and yttrium ions in the amorphous Al2 O3 –Y2 O3 films, the Al K α X-ray emission spectra and the X-ray absorption near edge structures (XANES) were measured. The average coordination number of aluminum ions in the amorphous films containing up to about 40 mol% Y2 O3 content was 5, that is a mixture of 4-fold- and 6-fold-coordinated states. In the region of more than about 50 mol% Y2 O3 , the fraction of the 6-fold-coordinated aluminum ions increased with increasing Y2 O3 content, while the results led to the conclusion that the coordination number of yttrium ions was always 6, regardless of composition. These results indicate that, in amorphous films in the system Al2 O3 –Y2 O3 , the change of the coordination state of aluminum ions has an important effect on physical properties. 相似文献
4.
The thermal expansion of the skeletal framework was essentially zero for NaZr2 (PO4 )3 -type compounds; the interstitialion, e.g., Na+ , was primarily responsible for the total thermal expansion. The composition dependence of the thermal expansion is discussed in terms of the amounts, crystallographic sites, and ionic radii of the interstitial ions. The mechanism which results in low thermal expansion was clarified, particularly for KZr2 (PO4 )3 , in which a larger ion is substituted for Na+ , and NbZr(PO4 )3 , which does not contain Na+ . Polycrystalline ceramics formed from these crystals might be useful as thermal-shock-resistant materials. 相似文献
5.
Low-thermal-expansion ceramics having arbitrary thermal expansion coefficients were synthesized from homogeneous solid solutions in the system KZr2 (PO4 )3 ─KTi2 (PO4 )3 (KZP–KTP). Dense and strong ceramics were fabricated by sintering at 1100° to 1200°C with 2 wt% MgO. The thermal expansion coefficient increased from 0 to +3 × 10−6 /°C with increasing x in KZr2 − x Tix (PO4 )3 (KZTP). In addition, a functionally gradient material with respect to thermal expansion was prepared by forming a series of KZTP solid solutions in a single ceramic body. By heating a pile of KZP and KTP ceramics in contact with each other, KZP and KTP bonded together to form a KZTP gradient solid solution near the interface. 相似文献
6.
The coordination and bond character of the cations in amorphous SiO2 -Al2 O3 films prepared by rf sputtering were examined by studying chemical shifts in the SiK and AlK X-ray emission spectra. The coordination number of Si ions in these films was always 4, regardless of composition, whereas the average coordination number of Al ions changed from 4 to 5, depending onAl2 O3 content. TheSi-O-Al bond type seemed to appear as Al2 O3 was introduced into amorphous SiO2 films or vice versa. 相似文献
7.
Transmission electron microscopy (at 100 and 1000 kV potential) and analytical scanning transmission electron microscopy were used to study α-Al2 03 second-phase particles and their interactions with grain boundaries in two high-conductivity Y2 03 /Yb2 03 stabilized zirconia ceramics containing deliberate additions of the alumina as a sintering aid. Most of the Al2 03 particles were intragranular and microanalysis showed that they contained inclusions rich in Zr or Si plus Zr. Al2 O3 particles at grain boundaries were frequently associated with amorphous cusp areas rich in Si and Al. The results suggest that the Al2 03 acts as a scavenger for SiO2 , removing it from grain-boundary localities. A model is proposed whereby this process occurs as the boundaries meet the second-phase particles, assisted by rapid grain-boundary diffusion. Such an ZrO2 -Al2 O3 -SiO2 interaction and partitioning is predicted thermodynamically and offers a possible explanation for the improvements in ionic conductivity brought about by Al2 O3 additions, as reported in the literature. 相似文献
8.
C. K. CHYUNG 《Journal of the American Ceramic Society》1969,52(5):242-245
The kinetics of secondary grain growth in a Ti02 -nucleated β-spodumene solid-solution glass-ceramic was studied. The thermal stability of the grains was excellent. Grain growth followed the cube-root-of-time law. The activation energy of the grain boundary migration was 55 ± 10 kcal/mol. Grain growth inhibition due to Ti02 precipitates and the residual glassy phase was closely examined. The excellent thermal stability of the grains is due to grain growth inhibition by the residual glassy phase, not by rutile precipitates. It is suggested that the diffusion of A2+ , and probably the simultaneous diffusion of Li+ , through the residual glass is the rate-limiting process for the grain boundary migration. 相似文献
9.
Chaitanya K. Narula M. Matti Maricq Brian G. Demczyk Irving T. Salmeen Willes H. Weber 《Journal of the American Ceramic Society》1993,76(11):2727-2733
Irradiation of Ti[N(CH3 )2 ]4 by the 1.064-μm line of a pulsed Nd: YAG laser in the presence of TiO2 , Al2 O3 , or Si3 N4 particles has been found to form amorphous deposits on the oxide particles. The resulting materials can be processed into TiN/TiO2 , TiN/Al2 O3 , or TiN/Si3 N4 composites with the TiN component on the surface of the particles. The powders have been characterized by Raman spectroscopy and X-ray powder diffraction studies. The surface analysis of the composites by X-ray photoelectron spectroscopy and high-resolution electron microscopy is presented. 相似文献
10.
The third-order nonlinear optical susceptibilities, X(3) , of the xLaO1.5 ·(100 – x)TeO2 binary glasses have been measured by the third harmonic generation (THG) method. In order to investigate the origin of high-intensity third harmonic generation, the various optical properties, such as nonlinear refractive index ( n 2 ), Abbe number ( v d ), dispersion energy ( E d ), average excitation energy ( E 0 ), (energy gap ( E g ), and polarizability (αm ), have been estimated from the refractive index and UV-visible absorption spectrum measurements. The linear refractive index, polarizability, and E d / E 0 2 increased, and Abbe number and energy gap decreased, with increasing LaO1.5 content. The nonlinear optical susceptibility X(3) is discussed in relation to these optical parameters. 相似文献
11.
A single-phase material (HfMg)(WO4 )3 with an orthorhombic structure, A2 (WO4 )3 -type tungstate, has been successfully prepared for the first time by the calcination of HfO2 , MgO, and WO3 , substituting Hf4+ and Mg2+ for A3+ cations in A2 (WO4 )3 . The new material shows a negative thermal expansion coefficient of approximately −2 ppm/°C from room temperature to 800°C. The mechanism of negative thermal expansion is assumed to be the same as that of Sc2 (WO4 )3 . 相似文献
12.
Mari Lou Balmer Hellmut Eckert Nandini Das Fred F. Lange 《Journal of the American Ceramic Society》1996,79(2):321-326
The local environment of the aluminum atoms in a series of metastable Zr(1− x ) Al x O(2− x/ 2) crystalline materials (0.08 ≤ x ≤ 0.57), prepared by diffusion-limited crystallization of amorphous precursors, has been determined by 27 Al magic angle spinning nuclear magnetic resonance (MAS NMR). Results show the existence of aluminum in 4-, 5-, and 6-fold coordination in both the amorphous and crystalline states. Although the relative amounts of each type of coordination show no compositional dependence in the amorphous state, the results for the crystalline materials show a systematic decrease in the average aluminum coordination number with increasing aluminum content. Comparisons of MAS NMR results between pure Al2 O3 precursors and Zr (1- x ) Al x O(2- x /2) crystalline materials processed under similar conditions show a profound effect of ZrO2 on the coordination environment of the aluminum atom. Both a random distribution model and a model that assumes small-scale clustering of aluminum ions are considered to explain the trends in the type of aluminum coordination as a function of composition. 相似文献
13.
Monika Agarwal Mark R. de Guire Arthur H. Heuer 《Journal of the American Ceramic Society》1997,80(12):2967-2981
Undoped or Y2 O3 -doped ZrO2 thin films were deposited on self-assembled monolayers (SAMs) with either sulfonate or methyl terminal functionalities on single-crystal silicon substrates. The undoped films were formed by enhanced hydrolysis of zirconium sulfate (Zr(SO4 )·4H4 O) solutions in the presence of HCl at 70°C. Typically, these films were a mixture of two phases: nanocrystalline tetragonal- ( t -) ZrO2 and an amorphous basic zirconium sulfate. However, films with little or no amorphous material could be produced. The mechanism of film formation and the growth kinetics have been explained through a coagulation model involving homogeneous nucleation, particle adhesion, and aggregation onto the substrate. Annealing of these films at 500°C led to complete crystallization to t -ZrO2 . Amorphous Y2 O3 -containing ZrO2 films were prepared from a precursor solution containing zirconium sulfate, yttrium sulfate (Y2 (SO4 )3 8·H2 O), and urea (NH2 CONH2 ) at pH 2.2–3.0 at 80°C. These films also were fully crystalline after annealing at 500°C. 相似文献
14.
The precursor [NH4 ]2 [Ti(catecholate)3 ] · 2H2 O is known to react with Ba(OH)2 · 8H2 O in an acid/base process that generates Ba[Ti(catecholate)3 ] · 3H2 O, a compound which undergoes low-temperatue calcination to produce BaTiO3 powder. Attempts to develop similar routes to PbTiO3 have been frustrated, since lead(II) hydroxide does not exist. The amphoteric yellow PbO and the basic oxide, Pb6 O(OH)6 4+ , are both insufficiently basic to react with [NH4 ]2 [Ti(catecholate)3 ] · 2H2 O. Based on the large sizes of both the [Ti(catecholate)3 ]2- anion and the Pb2+ cation, a precipitation method has been developed in which lead nitrate and [NH4 ]2 [Ti(catecholate)3 ] · 2H2 O are added together in an aqueous medium causing precipitation and leaving only NH4 NO3 in solution. The lead-titanium-catecholate complex that forms in this manner undergoes low-temperature pyrolysis to produce PbTiO3 . SEM indicates a submicrometer ultimate crystallite size. 相似文献
15.
HIROSHI HIRASHIMA KOTA NISHII TETSURO YOSHIDA 《Journal of the American Ceramic Society》1983,66(10):704-708
The dc conductivities (σ) of V2 O5 -P2 O5 glasses containing up to 30 mol% TiO2 were measured at T=100° to ∼10°C below the glass-transition temperature. Dielectric constants from 30 to 106 Hz, densities, and the fraction of reduced V ion were measured at room temperature. The conduction mechanism was considered to be small polaron hopping between V ions, as previously reported for V2 O5 -P2 O5 glass. The temperature dependence of σ was exponential with σ = σ0 exp(-W/kT ) in the high-temperature range. When part of the P2 O5 was replaced by TiO2, σ increased and W decreased. The hopping energy depended on the reciprocal dielectric constant which, in this case, increased with increasing TiO2 content. 相似文献
16.
The grain size-microcracking relation was examined for low thermal expansion NaZr2 (PO4 )3 family ceramics. By measurements of the strength, Young's modulus, thermal expansion, and grain size of polycrystalline ceramics sintered at appropriate conditions, the critical grain size for microcracking was determined. The critical grain size was proportional to the inverse square of the maximum thermal expansion difference. 相似文献
17.
The compositional range for glass formation below 1600°C in the Sm2 O3 ─Al2 O3 ─SiO2 system is (9–25)Sm2 O3 ─(10–35)Al2 O3 ─(40–75)SiO2 (mol%). Selected properties of the Sm2 O3 ─Al2 O3 ─SiO2 (SmAS) glasses were evaluated as a function of composition. The density, refractive index, microhardness, and thermal expansion coefficient increased as the Sm2 O3 content increased from 9 to 25 mol%, the values exceeding those for fused silica. The dissolution rate in 1 N HCl and in deionized water increased with increasing Sm2 O3 content and with increasing temperature to 70°C. The transformation temperature ( T g ) and dilatometric softening temperature ( T d ) of the SmAS glasses exceeded 800° and 850°C, respectively. 相似文献
18.
The composition (0.65Zn,0.35Mg)2 SiO1 was investigated. Its thermal expansion was 32 × 10-7 /°C from room temperature to 1000°C. Modulus of rupture was approximately 7000 psi between room temperature and 800°C, whereas Young's modulus held at approximately 11 × 10° psi over the same range. The substitution of 0.35 m oles Mg++ for Zn++ in Zn2 Si04 causes little change in many of the physical properties, but the solid solution sinters much more readily than pure Zn2 Sio4 . The willemite solid solution studied has very good thermal shock resistance between room temperature and 1000°C. 相似文献
19.
Isshu Sato Yoshitaka Ichikawa Junji Sakanoue Mamoru Mizutani Nobuyasu Adachi Toshitaka Ota 《Journal of the American Ceramic Society》2008,91(2):607-610
A ceramic composite mimicking the pervasively cracked microstructure of flexible sandstone (itacolumite) was successfully synthesized by sintering two ceramic materials with different thermal expansion coefficients. A combination of granular KZr2 (PO4 )3 (high thermal expansion) and powdered KAlSi2 O6 (low thermal expansion) resulted in a material with a jigsaw-like three-dimensional cracking microstructure similar to that of itacolumite. The synthesized composite was found to exhibit ductile deformation. 相似文献
20.
Kathleen B. Alexander Fred J. Walker Rodney A. McKee Fred A. List III 《Journal of the American Ceramic Society》1990,73(6):1737-1743
Titanium oxide/aluminum oxide films have been deposited using molecular beam epitaxy methods and characterized by reflection high-energy electron diffraction and transmission electron microscopy techniques. Growth on silicon substrates below 973 K resulted in primarily amorphous multilayers. At 1323 K, the deposition of titanium in an oxygen atmosphere on (0001) Al2 O3 substrates resulted in films of Ti2 O3 . These films consisted of small domains, up to 60 nm, slightly misoriented from a [1120] ∥ [1120] orientation relationship. Two variants of Ti2 O3 were observed due to multiple positioning during growth. Closing the titanium shutter during growth resulted in an oriented TiO2 film. 相似文献