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1.
The influence of the size of Y2O3 powder particles on the structure formation and densification of Nd3+:Y3Al5O12 laser ceramics has been studied. It is shown that the use of 50- and 100-nm yttrium oxide particles makes it possible to synthesize single-phase yttrium aluminum garnet at temperatures of 1200 and 1500°C, respectively, whereas in the case of 5000-nm yttrium oxide particles 2-h exposure at a temperature of 1500°C yields only 80 wt % of the Nd3+:Y3Al5O12 phase. Bulk swelling of pressed samples during sintering of 2.94Y2O3-0.06Nd2O3-5Al2O3 powders with the size ratio of the initial particles R(Al2O3/Y2O3) ~ 5 is observed. The application of different-sized powders (R ~ 2.5) provides quantitative ratios between phases in the 3Y2O3-5Al2O3 system at which shrinkage in a temperature range of 20–1500°C is dominant. Laser ceramics 0–2 at % Nd3+:Y3Al5O12 have been obtained by the solid-phase sintering of oxide powders (R ~ 2.5). The slope efficiency for 1 at % Nd3+:Y3Al5O12 laser ceramics is found to be 33%. 相似文献
2.
The polarity of rough and smooth grains in textured aluminum nitride boules were analyzed by transmission electron microscopy. Specifically, convergent beam electron diffraction method was applied to determine polarity. The grains corresponding to smooth and rough surfaces were identified as having Al and N polarities, respectively. Aluminum oxide (Al 2O 3) was observed to form at the grain boundaries. The oxide may precipitate due to the low mutual solubility between Al 2O 3 and AlN at the high crystal growth temperature (∼2000°C). Oxygen may be the cause of polarity inversion that leads to the formation of Al and N polar grains. 相似文献
3.
Bismuth sodium titanate (abbreviated as BNT) based solid solution, [Bi 0.5(Na 1‐x‐yK xLi y) 0.5]TiO 3 (0 < x + y < 1) ceramics, was invented in our group. These ceramics, which are considered as new candidates for lead‐free piezoelectric materials, were prepared by conventional ceramic sintering technique. The results of X‐ray diffraction show that the ceramics possess a single perovskite phase. The relations of the sintering conditions and the microstructures of the ceramics were studied. It was found that the optimized sintering condition is at 1100‐1150 °C for 2‐3 h, the grains of the ceramics have very regular shape, and the grain size of the ceramics is in the range of 1.3‐2.2 μm. These ceramics with the compositions of high amount of K + and low amount of Li + have relatively large piezoelectric charge constant ( d33), and can be put into practical applications. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
4.
The microhardness and fracture toughness of laser nanocrystalline ceramics based on the cubic oxides Y 2O 3 and Y 3Al 5O 12 are determined experimentally. It is shown by comparative measurements that the fracture toughness and microhardness of Y 2O 3 ceramics exceed the corresponding parameters of Y 2O 3 single crystals by factors of 2.5 and 1.3, respectively. The fine morphology of grains and grain boundaries in fractures is investigated. It is ascertained that changes in the mechanical properties of the nanocrystalline ceramics under study are related to both the sizes and structure of grains and the structure of grain boundaries. It is suggested that twinning processes determine the mechanisms of formation of nanocrystalline ceramics. 相似文献
5.
Nanocrystalline holmium aluminium garnet (Ho 3Al 5O 12) has been prepared for the first time by modified Pechini's reaction after sintering the precursor gel at 1223 K. The nanomaterial has been characterized by X‐ray diffraction (XRD), selected area electron diffraction (SAED) and high resolution transmission electron microscopy (HRTEM). The XRD pattern confirms the formation of single‐phase Ho 3Al 5O 12; the average size of the nanoparticles has also been determined. X‐ray photoelectron spectroscopy (XPS) has been used to study the chemical composition and bonding in the as‐prepared samples. The binding energies of core‐level electrons in Ho, Al and O in the title material have been found slightly shifted compared to the values of the respective elements. DC magnetic susceptibility has been measured in the temperature range 2 – 260 K. Low effective magnetic moment of Ho 3+, μ eff = 1.35 µ B and Weiss constant have been derived from the inverse magnetic susceptibility–temperature linear plot. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
6.
Mesoporous Al 2O 3 were positively synthesized via treatment of the freshly precipitated amorphous alumina gel using aluminium sulphate as aluminium source, and sodium dodecyl sulphate (SDS) as structure‐directing agent (SDAs). The microstructures, morphologies and textural properties of the as‐prepared materials were characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM) and thermo gravimetric analysis (TG‐DTA). The calcined product at 600 °C was highly porous in nature having a BET surface area of 42 m 2/g. These porous Al 2O 3 exhibits excellent adsorption performance for Congo red and the corresponding decolourisation efficiencies reached 99% in just 15 min at 27 °C. The subsequent calcined product at 1200 °C is the alpha alumina single crystal hexagonal platelets with rhombohedral crystallization. 相似文献
7.
Orientation relationships of aluminium nitride on sapphire (112 6) AlN/(011 2) Al 2O 3 have been defined more exactly by X-ray diffractometry techniques. It has been found that, depending on the substrate misorientation from the surface plane (011 2), there can exist two kinds of azimuthal orientation of the epitaxial layer of AlN, namely, the projection of [0001] AlN on plane (011 2) Al 2O 3 can coincide either with [2 110] Al 2O 3 or with [21 1 0] Al 2O 3 direction. The vector field of the epitaxial layer inclination relative to the substrate misorientation has been drawn. The symmetry of this field obeys Neumann's rule. The epitaxial layer orientation has been found to depend on the sapphire substrate misorientation in direction [21 1 0]. 相似文献
8.
For the preparation and transformation sequence in the system Y 4O 3–Al 2O 3 the sintering of homogeneously mixed oxide powders was chosen. The constituents of the Y 4Al 2O 9 phase were determined by quantitative phase analysis with the method of inner standards. Corresponding gauge curves for the conditions of the temperatures of sintering were drawn. At low temperatures appears as first in the whole molar range the (2:1) phase, i.e. Y 4Al 2O 9. With increasing temperature and sintering time the yield of this mixed crystal phase depends on the concentration of the oxide components in the powder mixture of the start materials. In flux mixtures of the components PbO, PbF 2, and B 2O 3 and despite suitable nucleation it was not possible to obtain this compound. In the melt the compound Y 4Al 2O 9 was prepared frequently in near molar conditions. Also a glass was prepared with (2:1) stoichiometry. Single crystals were identified by X-rays. 相似文献
9.
Transparent 0.1 at.%Cr,1.0 at.%Nd:YAG (Y 3Al 5O 12) ceramics were fabricated by a solid-state reaction and vacuum sintering with CaO as a charge compensator and tetraethyl orthosilicate (TEOS) as a sintering aid using high-purity powders of Al 2O 3, Y 2O 3, Nd 2O 3 and Cr 2O 3. The mixed powder compacts were sintered at 1800 °C for 5 h and 30 h under vacuum. The optical transmittance of the Cr,Nd:YAG ceramics sintered at 1800 °C for 5 h and 30 h is ∼63% and ∼78% in the infrared wavelengths, respectively. The two samples exhibit pore-free structures and the average grain size is about 10 and 20 μm. For the sample sintered at 1800 °C for 5 h, the dominant fracture mechanism is the transgranular fracture. With increase of holding time up to 30 h, the ratio of intergranular fracture surfaces increase and more Cr 3+ ions in the Cr,Nd:YAG ceramic transform to Cr 4+. High-quality Cr 4+,Nd 3+:YAG transparent ceramics may be a potential self-Q-switched laser material. 相似文献
10.
This study examined the potential applications of microwave dielectric properties of La (1‐2x/3)Ba x(Mg 0.5Sn 0.5)O 3 ceramics in rectenna. The La (1‐2x/3)Ba x(Mg 0.5Sn 0.5)O 3 ceramics were prepared by the conventional solid‐state method with various sintering temperatures. An apparent density of 6.62 g/cm 3, a dielectric constant of 20.3, a quality factor of 51,700 GHz, and a temperature coefficient of resonant frequency of ‐78.2 ppm/K were obtained for La 2.98/3Ba 0.01(Mg 0.5Sn 0.5)O 3 ceramics that were sintered at 1550 °C for 4 h. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
11.
Microhardness and fracture toughness of highly transparent Y 3Al 5O 12-and Y 3Al 5O 12: Nd 3+-based nanocrystalline ceramics are measured for the first time. For the Y 3Al 5O 12: Nd 3+ laser ceramics, the use of a longitudinal scheme with a diode-laser pumping at a wavelength of 1.3186 mm ( 4 F 3/2 → 4 I 13/2 channel) enabled one to attain an output power of continuous-wave lasing of ~3.7 W with 35% efficiency. 相似文献
12.
The porous glasses were prepared by a conventional phase separation method using coal fly ash as a raw material, and the properties of these porous glasses were investigated. The composition of coal fly ash is basically composed of SiO 2–Al 2O 3–Fe 2O 3–CaO system and the SiO 2–B 2O 3–Al 2O 3–CaO–Na 2O system of glass was chosen as base glass composition. The pore diameter increases proportional to cube root of heating time ( t1/3), however, the early stage of phase separation is not clear. It is estimated that the rate determining step may be the diffusion process of structural units involving oxygen ions and the phase separation may take place by the nucleation and growth mechanism, and the relatively larger pores of above 1 μm can be obtained easily. The chemical composition of porous glasses is SiO 2–B 2O 3–Al 2O 3(–CaO–Na 2O). A relatively large amount of fly ash (>40%) can be used successfully for the preparation of porous glass. 相似文献
13.
Crystallization and dielectric properties of typical low temperature co-fired ceramics (LTCC) consisting of calcium zinc aluminoborosilicate glass and Al 2O 3 filler were investigated by substituting the Al 2O 3 filler partially with Li 2O at the levels of 2-10 wt%. Depending on the content of Li 2O, densification was found significantly affected by early crystallization that resulted from the formation of unexpected crystalline phases including LiAlSiO 4, Ca 2SiO 4, LiAlO 2, and LiAlSi 3O 8. The effect of hindering sintering via earlier crystallization became enormous regardless of firing temperature when >5 wt% Li 2O substitution occurred. It was observed that the substitution of 2 wt% Li 2O for Al 2O 3 was beneficial in producing promising performance at the low temperature of 750 °C, which can be highlighted with k ∼ 8.7 and tan δ ∼ 0.009 at 1 MHz. 相似文献
14.
In this paper, Tb 3+/Sm 3+ co-doped 38B 2O 3―31Al 2O 3―31SrO glass was successfully prepared. After heat treatment, single crystal phase SrAl 2B 2O 7 was precipitated from the parent glass. DTA data showed the glass transition temperature at 625 °C and a sharp exothermic peak at 860 °C. XRD patterns demonstrated a regular evolution from glass to glass ceramics with higher treatment temperature and longer treatment time. From the XRD patterns, we supposed that Tb 3+/Sm 3+ ions can be most likely contained in the crystal phase. The photoluminescence spectra showed that the crystallization can enhance the emission intensity significantly and there could be an optimum crystallization degree to get the strongest luminescence in glass ceramics. The light scattering of devitrification sample can vary the intensity ratio of Sm 3+ and Tb 3+ emission. Therefore, as a potential route, rare earth ions doped glass ceramics could be a further research direction of luminescence glasses for white light emitting diodes application. 相似文献
15.
ZnO:Al ceramics (Zn:Al, 0.95:0.05) were prepared by using sol‐gel derived nanocrystalline powders. XRD patterns of the doped ceramics revealed the existence of both zincite (JCPDS 36‐1451) and gahnite (JCPDS 5‐0669) phases. Gahnite phase (ZnAl 2O 4) was segregated along the ZnO grain boundaries. At the sintering temperature of 1200 °C, relative density of the undoped and Al doped ceramics were measured as 0.695 and 0.628, respectively. Both grain size and relative density of the ceramics decreased with Al doping. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
16.
Samples of the magnetic glass–ceramics SiO 2–BaFe 12O 19 were obtained from mixtures of Fe 2O 3–BaSO 4–SiO 2–Na 2CO 3–CaCO 3 following a two-step route. The samples were characterized using XRD analysis and scanning electron microscopy, and their room temperature magnetization hysteresis loops were measured. It was found that the magnetic phase was completely developed in the precursor BaFe 12O 19 material when it was calcinated above 1000 °C. The size of the particles of the BaFe 12O 19 phase depends on the thermal treatment conditions and on the SiO 2 concentration. The magnetic data showed that the high value of the coercive magnetic field is preserved despite the fact that both the remanent and the saturation magnetizations diminish substantially. 相似文献
17.
In the system BaO-Al 2O 3-SiO 2 a metastable solid solution Ba 1−0,5xAl 2−xSi 2+xO 8 next two stable and one metastable modification of composition BaAl 2Si 2O 8 was observed. The discrete differences in nucleation behaviour and anisotropy of crystal growth of these crystalline phases favoury the formation of the solid solution. The production of defined crystals of metastable solid solution or of the needle-shaped stable low temperature modification is of relevance for the thermal stability of ceramics and glass ceramics. 相似文献
18.
The floating zone growth of magneto‐optical crystal YFeO 3 has been investigated. The polycrystalline feed rod was prepared by a pressure of 250MPa and sintering at about 1500°C. A crack‐ free YFeO 3 single crystal has been successfully grown. The crystal preferred to crystallize along <100> direction with about 10° deviation. The X‐ray rocking curve of the crystal has a FWHM of 24 arcsec, confirming the high crystal quality of the sample. The (100) plane was etched by hot phosphoric acid and the dislocation density was about 10 4/cm 2. A thin outer layer with Y 2O 3‐rich composition was found at the periphery of as‐grown crystals, which was attributed to the Fe 2O 3 evaporation during growth. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
19.
Crystals listed in the JCPDS card in the BaO‐B 2O 3‐Al 2O 3 and BaO‐B 2O 3‐Ga 2O 3 systems are of interest from a viewpoint of the Second Harmonic Generation (SHG). Ba 5Al 4B 12O 29 and Ba 5Ga 4B 12O 29 are promising new crystals with SHG activity and with congruent melting mode. These crystals can be grown by the Czochralski method with a size of 3 × 3 × 0.1‐1mm. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
20.
Based on the data of X‐ray phase and microstructure analysis, the sample composition was optimized in order to provide maximum size of the textured macrograins of YBa 2Cu 3O 7‐δ and of the crystallites in the Y 2BaCuO 5‐BaCuO 2‐CuO, Y 2Cu 2O 5‐BaCuO 2 systems. The growth rate has been studied and the YBa 2Cu 3O 7‐δ growth activation energy has been calculated for the samples of Y 2BaCuO 5+3BaCuO 2+2.3CuO, Y 2BaCuO 5+3BaCuO 2+0.6CuO, and Y 2Cu 2O 5+3.5BaCuO 2 compounds in the temperature range of 1240‐1270K for the case of use of the Y 2Cu 2O 5 and Y 2BaCuO 5 precursors with an average grain diameter of 10 μm and 1mm. A crystallization mechanism of YBa 2Cu 3O 7‐δ in the Y 2BaCuO 5‐BaCuO 2‐CuO and Y 2Cu 2O 5‐BaCuO 2 systems in the case of different sizes of Y 2BaCuO 5 and Y 2Cu 2O 5 precursor grains was proposed and validated. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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