Compositional segregation usually has negative effects on the growth of solid solution ferroelectric single crystals of Pb(In1/2Nb1/2)O3‐Pb(Mg1/3Nb2/3)O3‐PbTiO3 (abbr. PIN‐PMN‐PT or PIMNT). A modified Bridgman method was adopted in this work to control the segregation and improve the compositional homogeneity significantly. The characteristic of this work is to use multiround growths and gradient composition raw materials in order to keep the PbTiO3 concentration constant during the crystal growth. As an example, the two‐round growth of ternary PIN‐PMN‐PT single crystal is conducted in the same Pt crucible with gradient raw materials, where the first‐round boule was used as the seed crystal for the second‐round growth. Our results show that the as‐grown (Ф80 mm × 270 mm) PIN‐PMN‐PT crystals exhibit higher phase transition temperatures (Tc∼180 °C, Tr/t∼110 °C) and larger coercive field (Ec∼5–5.5 kV/cm), which are much better than the performances of Pb(Mg1/3Nb2/3)O3‐PbTiO3 crystals, and similar dielectric and piezoelectric performances (ε∼5000, tanδ∼1.25%, d33∼1500 pC/N, kt∼60%). And about 85 percent of the crystal boule grown by the two‐round growth technique could maintain its compositions around the morphotropic phase boundary. 相似文献
Single crystals of the composition PbFe1/2Ta1/2O3 are grown by the method of mass crystallization from flux. It is established that, unlike the PbFe1/2Ta1/2O3 ceramic, the synthesized single crystals possess pronounced relaxor properties: the maximum of the dielectric constant is diffuse and its temperature, Tm, increases by more than 70 K with an increase in the frequency from 102 to 106 Hz. It is assumed that the unusual properties of the PbFe1/2Ta1/2O3 crystals are caused by mesoscopically inhomogeneous compositional ordering and comparatively high conductivity providing favorable conditions for the appearance of the volume-charge and thermal electron polarization. 相似文献
Structure analysis of polycrystalline BaMg1/3Ta1/3Nb1/3O3 ceramics has been carried out using the Rietveld technique, wherein the B cations (Mg, Ta, and Nb) have the same occupancy with a size difference and charge imbalance. The compound has an ordered
trigonal structure as well as a disordered cubic phase depending on the preparation temperature. The weight percentage of
the ordered phase is found to increase with a rise in the calcination temperature.
Published in Russian in Kristallografiya, 2006, Vol. 51, No. 2, pp. 259–263.
The text was submitted by the authors in English. 相似文献
The influence of grain size on the vibrational properties of Mn2O3 nanocrystals has been investigated by transmission electron microscopy, Raman and infrared (IR) spectroscopy. It is found that the vibrational properties are sensitively dependent on the grain sizes of Mn2O3 nanocrystals. Raman spectra studies indicate that with decreasing grain sizes, allowing the transition of phonons with q ≠ 0 contributes to the Raman spectrum, which leads to the broadening of the Raman peaks in the lower frequency region. IR spectra exhibit the remarkable differences in the shapes with different grain sizes of Mn2O3 nanocrystals. The shape of the band in the 570–670 cm−1 ranges is strongly evocative of transverse-optical (TO) and longitudinal-optical (LO) splitting. This splitting appears more and more clear with the decreasing grain size of Mn2O3 nanocrystals. 相似文献
Infrared and Raman spectra were measured for a series of glass compositions in the binary B2O3-GeO2 system at room and elevated temperatures. No coordination changes were detected from spectral analysis for either boron or germanium with concentration or temperature changes. Interpretation of the vibrational spectra indicated that both boroxol rings and BO3-triangular units were present as the basic units in glasses with higher B2O3 concentrations. Only BO3-triangular units were detected as the basic units in glasses with lower B2O3 concentrations. Raman spectra of glasses measured at higher temperatures (>Tg) indicated that their boroxol ring concentrations decreased as a function of temperature. The enthalpy for ring rupture in 35GeO2–65B2O3 glass was 7.7 kcal/mol. Also, spectral analysis indicated that the boroxol ring concentrations of these glasses at room temperature were dependent upon their previous heat treatments. 相似文献
Liquids with the base compositions (16 − x/2)Na2O · xNaF · 10CaO · 74SiO2 (x = 0, 1, 3, and 4) and (10 − x/2) · Na2O · xNaF · 10CaO · yAl2O3 · (80 − y)SiO2 (x = 0, 1, 3, 5 and y = 5 and 15) doped with 0.25 mol% Fe2O3 were studied by means of square-wave voltammetry in the temperature range from 1000 to 1500 °C. With increasing temperature, the redox equilibria were shifted to the reduced state. Also while increasing the alumina concentration, the Fe2+/Fe3+-redox equilibrium is shifted to the reduced state. In the soda-lime–silica melt the addition of fluoride shifts the equilibrium to the oxidized state, while in the aluminosilicate melts with 15 mol% Al2O3, the equilibrium is shifted to the reduced state. In the aluminosilicate melts with 5 mol% Al2O3, the equilibrium was not affected by the fluoride concentration. This is explained by the structure of the respective glass compositions. 相似文献
Glasses in the system BaO/Al2O3/B2O3 with and without the addition of platinum were melted. In one sample series, the BaO-concentration was varied while the ratio [Al2O3]/[B2O3] was kept constant. In another sample series, the [BaO]/[Al2O3]-ratio (= 0.9) was kept constant and the B2O3 concentration was varied. The samples were thermally treated at 720 °C for 24 h and subsequently at 780 °C for 4 h. In most thermally treated samples, the crystalline phase BaO · Al2O3 · B2O3 occurred. At some compositions, the platinum-doped samples showed larger concentrations of the crystalline phases. The most remarkable property of the obtained glass–ceramics is their zero or negative thermal expansion coefficient. Here, notable differences were observed: samples with fine grained microstructures showed thermal expansion coefficients approximately zero up to temperatures of around 80 °C. By contrast, samples with coarser microstructures and large spheroidal crystals exhibit negative expansion coefficients up to temperatures of around 280–375 °C. The thermal expansions of these samples were close to those of the mean thermal expansion of the unit cell of the BaO · Al2O3 · B2O3 phase. The thermal expansion of the fine grained samples was approximately equal to that of the crystallographic a-axis of the BaO · Al2O3 · B2O3 phase. 相似文献
The paper is concerned with solubility models for Y3Fe5O12 (YIG) and Gd3Ga5O12 (GGG) solved in PbO/B2O3 high temperature solutions containing Fe2O3 or Ga2O3 in excess. It is shown that a new extended eight-particle model Interprets well the literature data of the solubility of YIG as well as the DTA data of the solubility of GGG. Comparisons of solution enthalpies determined in terms of the single-molecule, eight-particle, and extended eight-particle model are carried out in dependence on the excess concentration of species containing iron or gallium, respectively. 相似文献
The paper deals with the solubility of (YSmLuCa)3 (FeGe)5O12 garnet in PbO—B2O3 flux. An anionic model explaining the effect of B2O3 on the solubility of rare earth garnet is suggested. This model is based on the assumption that PbO in the melted mixture of PbO, B2O3, Fe2O3, R2O3, CaO, GeO2 dissociates into Pb2+ and O2−. The oxygen anions react with the other oxides under the formation of BO33−, FeO33−, RO69−, CaO22− and GeO32− anions, until the equilibrium is established. The garnet is dissociated into the anions mentioned above. The validity of the model is verified by an agreement of the experimentally determined saturation temperatures of the melts for LPE of garnet layers with the Arrhenius-type expression of the solubility product of garnet where xi denotes the equilibrium concentrations of the anions in the melt and x° is the Ge content of the garnet film. 相似文献
