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1.
Splat and other rapid quenching techniques were applied to a systematic study of simple oxides, and four new pure oxide glasses were obtained (V2 O5 , TeO2 , MoO3 , and WO2 ). The high-temperature tetragonal form of WO3 coexists with a metastable short-range-order-only phase. The structure of a new metastable high-temperature phase, δ-Ta2 O6 , resembles δ-Nb2 O6 . Predominant phases found in quenched Al2 O3 belong to the γ-(spinel type) series. 相似文献
2.
Hongwu Xu Alexandra Navrotsky M. Lou Balmer Yali Su 《Journal of the American Ceramic Society》2002,85(5):1235-1242
The crystal structures for a suite of substituted pollucites with the compositions CsTi x Al1– x Si2 O6+0.5 x , 0 ≤ x ≤ 1, have been determined from Rietveld analysis of powder synchrotron XRD data. Our results indicate that the pollucite end member (CsAlSi2 O6 ) has a tetragonal structure (space group I 41 / a ), whereas all other compositions are cubic (space group Ia 3 d ). The increased symmetry for the titanium-substituted structures is presumably due to the incorporation of additional O2− anions (needed for compensating the charge imbalance between Ti4+ and Al3+ ), which effectively holds open the expanded cubic framework. In situ cooling experiments of the substituted phase CsTi0.1 Al0.9 Si2 O6.05 reveal a displacive transformation to the tetragonal structure at ∼230 K. This transformation is tricritical in nature and is analogous to the tetragonal-to-cubic transition in pollucite on heating. 相似文献
3.
Sangeeta D. Ramamurthi Zhengkui Xu David A. Payne 《Journal of the American Ceramic Society》1990,73(9):2760-2763
ZrO2 powder was prepared by a sol–emulsion–gel method at temperatures below 140°C from ZrO(NO3 )2 · n H2 O. The asprepared powder was amorphous, but crystallized into the tetragonal structure by 600°C. The metastable tetragonal powder (600°C) was comprised of ultrafine 4- to 6-nm size particles. On heat treatment, the tetragonal form completely transformed into the monoclinic state at 1100°C. Preliminary studies indicate good sinterability with densities greater than 94% at 1100°C and with a grain size of 0.25 μ. 相似文献
4.
Structural Changes of Scandia-Doped Zirconia Solid Solutions: Rietveld Analysis and Raman Scattering 总被引:1,自引:0,他引:1
Hirotaka Fujimori Masatomo Yashima Masato Kakihana Masahiro Yoshimura 《Journal of the American Ceramic Society》1998,81(11):2885-2893
Powder X-ray diffractometry (XRD) and Raman scattering measurements were used to study the structural changes of compositionally homogeneous metastable ZrO2 solid solutions induced by ScO1.5 doping. The crystal structures of monoclinic, tetragonal, cubic, and rhombohedral (Sc2 Zr7 O17 , ß-phase) solid-solution phases have been refined by using the Rietveld analysis of the XRD data at room temperature of arc-melted ZrO2 - X ScO1.5 ( X = 0, 2, …, 20, and 22 mol%) samples. The results can be interpreted as indicating that the structures of the monoclinic and tetragonal phases approach those of the tetragonal and cubic phases, respectively, by ScO1.5 doping. Raman scattering, as well as XRD, was useful to investigate the phase assemblage. Moreover, we could obtain Raman spectra of the ß-phase probably for the first time. 相似文献
5.
Tatsuo Kumagai Kazuhiro Hongo Hiroshi Kimura 《Journal of the American Ceramic Society》2004,87(4):644-650
Phase transformations during consolidation treatments of an attrition-milled amorphous yttria-partially-stabilized zirconia (Y-PSZ: ZrO2 –3 mol% Y2 O3 )–20 mol% Al2 O3 powder and the resulting microstructures have been investigated. A metastable cubic phase ( c -ZrO2 solid solution) together with an α-Al2 O3 phase is formed in the amorphous matrix by consolidation at temperatures below 1204 K. The metastable cubic phase transforms to a stable tetragonal phase ( t -ZrO2 solid solution) with an increase in the consolidation temperature. Fully dense bulk samples consisting of extremely fine tetragonal grains together with a small amount of α-Al2 O3 particles could be obtained by consolidation at temperatures above 1432 K. Important features concerned with the densification behavior are as follows: (1) Marked increase in the relative density occurs after cubic crystallization and subsequent cubic-to-tetragonal transformation. (2) All of the consolidated bulk samples show extremely fine grain structure with grain sizes of several tens of nanometers, irrespective of the consolidation temperature. (3) The regularity of the lattice fringe contrast in each tetragonal grain seems to be kept in the vicinity of grain boundaries. These results suggest that densification of the attrition-milled amorphous powder proceeds via superplastic flow and/or diffusional creep, rather than viscous flow of the initial amorphous phase before crystallization. 相似文献
6.
I. A. EL-SHANSHOURY V. A. RUDENKO I. A. IBRAHIM 《Journal of the American Ceramic Society》1970,53(5):264-268
Polymorphism in thin evaporated films of zirconium and hafnium oxides was investigated from 100° to 1500°C by electron diffraction and transmission electron microscopy. The films have metastable cubic structures at room temperature and at moderate temperatures. Zirconium oxide, depending on temperature, exists in cubic, tetragonal, and monoclinic forms, whereas hafnium oxide transforms directly from the cubic to the monoclinic structure. The transformation temperatures depend on the oxygen partial pressure. Air annealing of thin films of ZrO2 and HfO2 lowered the temperature of transformation of the tetragonal and the cubic structure into the monoclinic structure by about 150° and 100°C, respectively. The cubic/tetragonal transformation of ZrO2 is monotropic, whereas the tetragonal monoclinic transformation occurs by the typical nucleation and growth mechanism. Determination of grain size in ZrO2 at the tetragonal/monoclinic transformation temperature showed that the transformation occurs when a constant grain size of about 800 Å is reached. The oxygen partial pressure, grain size, and temperatures at which the metastable phases exist were correlated. The rate of grain growth is enhanced by increase in oxygen partial pressure. The accelerated transformation in air is attributed to rapid attainment of the critical size; grain boundary energy is an important controlling factor in transformation. 相似文献
7.
Wei-Chih Lee Yi-Fang Lee Min-Hui Tseng Chi-Yuen Huang Yu-Chun Wu 《Journal of the American Ceramic Society》2009,92(5):1069-1073
The crystal structure and ferroelectric properties of (1− x )(Bi0.5 Na0.5 )TiO3 – x Ba(Zr0.05 Ti0.95 )O3 (BNBZT x, x ≤12%) lead-free piezoelectric ceramics were studied. The distance between the centers of cations and anions ( d c–a ) as well as the lattice parameters was carefully investigated by Rietveld refinement on X-ray diffraction patterns. It was found that the crystal phase was determined by the amount of Ba(Zr0.05 Ti0.95 )O3 added, whereas the pure rhombohedral and tetragonal phases are observed in compositions containing x ≤4 and x ≥8%, respectively. A rhombohedral–tetragonal morphotropic phase boundary (MPB) was found at around BNBZT6, which showed a maximum and minimum d c–a at its rhombohedral and tetragonal phases, respectively. According to the present study, the ferroelectric properties show a strong dependence on their crystal phases. For the single-phase compositions, the remanent polarization ( P r ) generally increased with the value of d c–a while their coercive fields ( E c ) were determined by their lattice parameters. Nevertheless, the behavior in P r and E c for MPB compositions is related to not only the lattice parameter but also the composed phases. 相似文献
8.
Kallada Prabhakaran Rema Viswanathan Kumar 《Journal of the American Ceramic Society》2008,91(1):164-168
Hard piezoelectrics based on PZT with a composition near the morphotropic phase boundary (Pb0.94 Sr0.06 )(Zr0.53 Ti0.47 )O3 [PSZT] have been synthesized by the sol–gel method. The influence of B site aliovalent dopant Mn3+ on the crystal structure and electrical properties has been investigated. Mn3+ ions ( d 4 ) are found to change the crystal structure from tetragonal to rhombohedral as a result of Jahn–Teller distortion of the MnO6 octahedra and are therefore found to impart donor characteristics to PSZT. 相似文献
9.
Gan Feng Tu Zhi Tong Sui Qiang Huang Chang Zhen Wang 《Journal of the American Ceramic Society》1992,75(4):1032-1034
Y-PSZ ceramics with 5 wt% Al2 O3 were synthesized by a sol–gel route. Experimental results show that powders of metastable tetragonal zirconia with 2.7 mol% Y2 O3 and 5 wt% Al2 O3 can be fabricated by decomposing the dry gel powder at 500°C. Materials sintered in an air atmosphere at 1500°C for 3 have high density (5.685 g/cm3 ), high content of metastable tetragonal zirconia (>96%), and high fracture toughness (8.67 MPa.m1/2 ). Compared with the Y-PSZ ceramics, significant toughening was achieved by adding 5 wt% Al2 O3 . 相似文献
10.
A new phase was prepared from Bi2 O3 ·15 mol% PbF2 by heating it at 700°C and then quenching to room temperature. The crystal structure (tetragonal, a =0.765 and c = 1.77 nm, P42 /nmc) is related to that of the β-phase of Bi2 O3 by a supercell which is 3 times larger in the c direction. 相似文献
11.
Mari Lou Balmer Fred F. Lange Carlos G. Levi 《Journal of the American Ceramic Society》1994,77(8):2069-2075
Aqueous solutions of zirconium acetate and aluminum nitrate were spray pyrolyzed at 250°C and upquenched to different temperatures to yield metastable solid solutions of composition Zr(1− x ) Alx O(2− x /2) . An amorphous oxide forms first during pyrolysis which subsequently crystallizes as a single phase for x ≤ 0.57 (≤40 mol% Al2 O3 ). The crystallization temperature increased with Al2 O3 content. Electron diffraction, supported by Raman spectroscopy, indicates that the initial phase is tetragonal. At higher temperatures, the initial solid solation partitions to other metastable phases, viz., t -ZrO2 +γ-Al2 O3 , prior to achieving their equilibrium phase assemblage, m -ZrO2 +α-Al2 O3 . Partitioning yields a nanocomposite microstructure with grain sizes of 20–100 nm, compared to the 3 to 5 nm in the initial, single phase. Compositions containing 45 to 50 mol% Al2 O3 concurrently crystallize and partition. The structure selected during crystallization and the partitioning phenomena are discussed in terms of diffusional constraints during crystallization, which are conceptually similar to those operating during rapid solidification. 相似文献
12.
Hyunjung Shin Monika Agarwal Mark R. De Guire Arthur H. Heuer 《Journal of the American Ceramic Society》1996,79(7):1975-1978
Thin films of crystalline TiO2 were deposited on self-assembled organic monolayers from aqueous TiCl4 solutions at 80°C; partially crystalline ZrO2 films were deposited on top of the TiO2 layers from Zr(SO4 )2 solutions at 70°C. In the absence of a ZrO2 film, the TiO2 films had the anatase structure and underwent grain coarsening on annealing at temperatures up to 800°C; in the absence of a TiO2 film, the ZrO2 films crystallized to the tetragonal polymorph at 500°C. However, the TiO2 and ZrO2 bilayers underwent solid-state diffusive amorphization at 500°C, and ZrTiO4 crystallization could be observed only at temperatures of 550°C or higher. This result implies that metastable amorphous ZrTiO4 is energetically favorable compared to two-phase mixtures of crystalline TiO2 and ZrO2 , but that crystallization of ZrTiO4 involves a high activation barrier. 相似文献
13.
KURT NASSAU CHRISTINE A. WANG MICHAEL GRASSO 《Journal of the American Ceramic Society》1979,62(1-2):74-79
A twin-roller apparatus was used to quench 21 melts in the three pseudobinary systems and in the pseudoternary system composed of LiTaO3 , NaTaO3 , and KTaO3 . Glasses were obtained in all but the high-Na region. X-ray diffraction and differential thermal analysis studies of the metastable compositions showed that there were two metastable crystalline phases when the materials crystallized; one phase was a defect pyrochlore structure centered at KTaO3 and the other appeared at Li0.8 K0.2 TaO3 . The metastable phases subsequently transformed into the expected stable phases on heating. There is some evidence for a subsolidus two-glass region in the system (K,Na)TaO3 . 相似文献
14.
Pomin Su Anil V. Virkar Camden R. Hubbard O. Burl Cavin Wallace D. Porter 《Journal of the American Ceramic Society》1993,76(10):2513-2520
Gd2 O3 -doped Bi2 O3 polycrystalline ceramics containing between 2 and 7 mol% Gd2 O3 were fabricated by pressureless sintering powder compacts. The as-sintered samples were tetragonal at room temperature. Hightemperature X-ray diffraction (XRD) traces showed that the samples were cubic at elevated temperatures and transformed into the tetragonal polymorph during cooling. On the basis of conductivity measurements as a function of temperature and differential scanning calorimetry (DSC), the cubic → tetragonal as well as tetragonal → cubic → teansition temperatures were determined as a function of Gd2 O3 concentration. The cubic → tetragonal transformation appears to be a displacive transformation. It was observed that additions of ZrO2 as a dopant, which is known to suppress cation interdiffusion in rare-earth oxide–Bi2 O3 systems, did not suppress the transition, consistent with it being a displacive transition. Annealing of samples at temperatures 660°C for several hundred hours led to decomposition into a mixture of monoclinic and rhombohedral phases. This shows that the tetragonal polymorph is a metastable phase. 相似文献
15.
The effects of donor and acceptor doping on the piezoelectric properties of 18Pb(Mg1/3 Nb2/3 )O3 ·39PbZrO3 ·43PbTiO3 ternary solid solution have been investigated. The dopants influence in a pronounced way both the crystal structure and microstructure of the materials. The materials are transformed from the rhombohedral to the tetragonal structure, and the grain size is reduced when Nb 5+ cations are added. The crystal structures are transformed from the rhombohedral to the cubic structure, and grain growth is enhanced, when Mg 2+ cations are included. The values of K P and K are maximized for 1-mol%-Nb5+ -doped samples (K P = 0.69, K = 1152); the Q m factor and E c are optimized for 4-mol%-Mg2+ -doped samples ( Q m = 1534, E c = 0.56). 相似文献
16.
CHARLES A. SORRELL 《Journal of the American Ceramic Society》1973,56(12):613-618
Isothermal oxidation of tetragonal PbO in air produced multiphase assemblages with apparent equilibrium compositions which varied linearly with temperature from PbO1.548 at 286°C to PbO1.333 at 351°C. Oxidation at each temperature was relatively rapid to PbO1.40 and very slow from PbO1.40 to apparent equilibrium values. Pseudocubic PbO1+ x , with compositions between PbO1.41 and PbO1.57 , was indexed on a cubic unit cell at the lower O/Pb ratios and on a tetragonal unit cell at the higher ratios. Linear changes in lattice parameters and deviation from cubic symmetry accompanied reversible oxidation and reduction of the phase. Pseudocubic PbO1+ x was reduced irreversibly to Pb3 O4 below the composition PbO1.41 . Hexagonal PbO1+ x , with compositions between PbO1.333 and PbO1.41 , developed to a maximum of 60% at intermediate temperatures. The hexagonal phase oxidized irreversibly to pseudocubic PbO1+ x at lower temperatures and reduced irreversibly to Pb3 O4 at higher temperatures. The extent of oxidation at a given temperature was greater in PbO with a mean diameter of 0.52 μm than in PbO with a mean diameter of 2.89 μm, indicating a metastable assemblage. Linear variation of oxidation limits with temperature across the composition boundary between the PbO1+ x phases suggests that the free energies are equal at PbO1.41 , with the lower limit of pseudocubic PbO1+ x determined by tolerance of the structure for oxygen vacancies. 相似文献
17.
Yudong Hou Mankang Zhu Feng Gao Hao Wang Bo Wang Hui Yan Changsheng Tian 《Journal of the American Ceramic Society》2004,87(5):847-850
Pb(Zn1/3 Nb2/3 )0.20 (Zr0.50 Ti0.50 )0.80 O3 ceramics of pure perovskite structure were prepared by the two-stage method with the addition of 0–3.0 wt% MnO2 and their piezoelectric properties were investigated systematically. The MnO2 addition influences in a pronounced way both the crystal structure and the microstructure of the materials. The materials are transformed from the tetragonal to the rhombohedral structure, and the grain size is enhanced when manganese cations are added. The distortion of crystal structure for samples with MnO2 addition can be explained by the Jahn–Teller effect. The values of electromechanical coupling factor ( k p ) and dielectric loss (tan δ) are optimized for 0.5-wt%-MnO2 -doped samples ( k p = 0.60, tan δ= 0.2%) and the mechanical quality factor ( Q m ) is maximized for 1.0-wt%-MnO2 -doped samples ( Q m = 1041), which suggests that oxygen vacancies formed by substituting Mn3+ and Mn2+ ions for B-site ions (e.g., Ti4+ and Zr4+ ions) in the perovskite structure partially inhibited polarization reversal in the ferroelectrics. The ceramics with 0.50–1.0 wt% MnO2 addition show great promise as practical materials for piezoelectric applications. 相似文献
18.
We have observed a previously unreported metastable intermediate phase during the crystallization of magnesium metaphosphate (Mg(PO3 )2 ) glasses to the equilibrium ring phase, Mg2 P4 O12 . Our current hypothesis is that the metastable phase contains metaphosphate chains, as in other crystalline alkaline-earth metaphosphates. This type of phase could form by low-energy rearrangement of the polyphosphate chains in the glass structure. Thus, its formation might be favored at low temperatures where there is insufficient thermal energy to break the metaphosphate chains and form tetrametaphosphate rings. 相似文献
19.
Michiyuki Yoshida Yutaka Shinoda Takashi Akatsu Fumihiro Wakai 《Journal of the American Ceramic Society》2002,85(11):2834-2836
Ultrafine-grained monoclinic ZrO2 polycrystals (MZP) and 3-mol%-Y2 O3 -stabilized tetragonal ZrO2 polycrystals (3Y-TZP) were obtained by hot isostatic pressing (HIP). Both MZP and TZP were "high-purity" materials with impurities less than 0.1 wt%. The deformation behavior was studied at 1373 K, which was lower than the monoclinic ↔ tetragonal transition temperature. The stress exponent of 3Y-TZP with grain size of 63 nm was 3 in the higher stress region, and increased from 3 to 4 with decreasing stress. The deformation of MZP was characterized by a stress exponent of 2.5 over a wide stress range. The strain rate of 3Y-TZP was slower than that of MZP by 1 order of magnitude. It was suggested that either the doped yttrium or the difference in the crystal structure affected the diffusion coefficients of ZrO2 . 相似文献
20.
M. H. LEWIS J. METCALF-JOHANSEN P. S. BELL 《Journal of the American Ceramic Society》1979,62(5-6):278-288
Transmission electron microscopy, electron diffraction, and microprobe X-ray analysis were used to study crystallization of glasses in the systems Li2 O-SiO2 , BaO-SiO2 , and Li2 O-A12 O3 -SO2 . The ternary system, with 4 mol% TiO2 added to an Li2 O-Al2 O3 -4SiO2 composition, crystallizes with a simple morphology of equiaxed grains of the β-quartz metastable phase which transforms at higher temperatures to the stable β-spodumene structure. The binary systems exhibit a more complex crystallization morphology dictated by crystal anisotropy, temperature, impurity content, and susceptibility either to intermediate-phase formation (BaO-SiO2 ) or to liquid immiscibility (Li2 O-SiO2 ). The initial crystal growth units formed in these systems are frequently two-phase branched morphologies many micrometers in diameter. They may be recrystallized to form polycrystalline glass-ceramics with submicrometer grain sizes. 相似文献