P.L. Wang

Characteristics of Ca-α-sialon : Phase formation, microstructure and mechanical properties

Abstract Ca-α-Sialon (Ca x Si 12 -( m+n ) Al m+n O n N 16-n ,) ceramics with extensive compositions on the line of Si 3 N 4 –CaO:3AlN (where m =2 n ) ranged from x =0·3 up to x =2·0 were fabricated by hot-pressing. An exploration for Ca-α-Sialon involving reaction sequences, phase compositions, cell dimensions, microstructure and mechanical properties was carried out in the present work.

P-doped p-type ZnO films deposited on Si substrate by radio-frequency magnetron sputtering

P-doped ZnO films were deposited on n-Si substrate by radio-frequency magnetron sputtering. Hall measurements revealed that the films annealed in situ at 750°C in an oxygen ambient at a pressure of 1.3×10−3–3.9×10−3Pa showed p-type behavior with a hole concentration of 2.7×1016–2.2×1017cm−3, a mobility of 4–13cm2∕Vs, and a resistivity of 10.4–19.3Ωcm. Films annealed at 750°C in a vacuum or in oxygen ambient at higher pressures (5.2×10−3 and 6.5×10−3Pa) showed n-type behavior. Additionally, the p-ZnO∕n-Si heterojunction showed a diodelike I-V characteristic. Our results indicate that P-doped p-type ZnO films can be obtained by annealing in oxygen ambient at very low pressures.

In situ formation and rapid decomposition of Ti(BH4)3 by mechanical milling LiBH4 with TiF3

Mechanically milled 3LiBH(4)/TiF(3) mixture can rapidly release over 5 wt % hydrogen at moderate temperatures (70-90 degrees C) without undesired gas impurity. Structure analyses results show that the favorable dehydrogenation performance of the material should be associated with the in situ formation and rapid decomposition of an intermediate titanium borohydride (Ti(BH(4))(3)). These findings demonstrated a viable chemical activation approach for promoting hydrogen release from the thermodynamically stable borohydrides. Particularly, it shows the potential of transition metal borohydrides for hydrogen storage applications.

Estimation of the phase diagram for the ZrO2-Y2O3-CeO2 system

Abstract Comprehensive descriptions of the thermodynamic properties and experimental information in three oxide systems ZrO 2 –Y 2 O 3 , ZrO 2 –CeO 2 and Y 2 O 3 –CeO 2 are given and thermodynamic models for the calculation of these systems are discussed. The phase diagrams of the quasi-ternary ZrO 2 –Y 2 O 3 –CeO 2 system in the zirconia-rich corner are estimated at different temperatures with a substitutional model and Muggianus extrapolation. The equilibrium phase diagram calculation is extended to low temperatures, as well as the Gibbs free energy of the tetragonal, monoclinic and cubic phases of zirconia doped with yttria and ceria.

Mechanical properties of AlN-polytypoids: 15R, 12H and 21R

Abstract Mechanical properties of three types of AlN-polytypoids with Ln2O3(Ln=Nd,Sm) and Ln2O3:Al2O3=1:1, respectively, as sintering additives were studied. The results showed that the hardness increased with the AlN-polytypoid compositions shifting towards AlN-rich side, that was 21R having the highest hardness (12.7–14.4 GPa) and 15R the lowest values(11.5–12.8 GPa). The fracture toughness and flexural strength had no such close relationships to the type of AlN-polytypoids, which varied in a range of 3.8–4.8 MPa·m1/2 and 313–366 MPa (at room temperature), respectively. However, for the compositions with suitable amount of additives, the flexural strength greatly increased with increasing temperatures, especially for 15R and 12H. This characteristic was discussed on the basis of the fracture morphology observed by SEM.

Formation behavior of multi-cation α-sialons containing calcium and magnesium

Abstract The formation behavior of multi-cation α-sialons (α′) containing calcium and magnesium has been studied for the compositions M x Si 12−3 x Al 3 x O x N 16− x ( M =0.5 Ca+0.5 Mg) with x ranging from 0.3 to 1.4. It was found that the AlN-polytypoid phase coexists together with α-sialon in sintered samples when x is equal to or greater than 1.0 and the AlN-polytypoid content increases as the x -value increases. TEM results further revealed that most of the added Mg 2+ ion was incorporated into the sialons to form the magnesium AlN-polytypoid phase. The advantages of the formation of the magnesium AlN-polytypoid phase in multi-cation α-sialon materials are also discussed in this paper.

Direct formation of Na3AlH6 by mechanical milling NaH/Al with TiF3

Na3AlH6 can be directly formed by mechanical milling NaH/Al with TiF3 under hydrogen atmosphere. The hydrogenation fraction of NaH increases with increasing the milling time, and reaches up to 0.61 after 20 h milling. Thus-formed Na3AlH6 exhibits unexpected polymorphic transformation and decomposition behaviors. This, together with the unusual hydrogen storage performance of the mechanically prepared materials, provides us a suggestive perspective to probe the favorable modification of the thermodynamics of Na3AlH6 and nature of active Ti-species in Ti-doped NaAlH4

Study on the solid solubility of Al in the melilite systems R2Si3 − xAlxO3 + xN4 − x with R = Nd, Sm, Gd, Dy and Y

Abstract The solubility of aluminium in the nitrogen-containing melilite structure has been studied by preparation of specimens of the general formula R 2 Si 3 − x Al x O 3 + x N 4 − x with R = Nd, Sm, Gd, Dy and Y by hot pressing and pressureless sintering techniques in the temperature interval 1600–1750 °C. For elements with large ionic radii, i.e. R = Nd and Sm, up to one Si can be replaced by Al, but the solubility limits in melilite solid solutions decrease with decreasing the ionic radii. Consequently, yttrium-melilite had the lowest observed aluminium solubility (x ≈ 0.6) in rare earth elements-melilite solid solutions.

Formation behavior and microstructure of multi-cation α-sialons containing neodymium and ytterbium or yttrium

Abstract Multi-cation α-sialons containing neodymium and ytterbium, as well as neodymium and yttrium, were prepared by hot pressing at the temperatures ranging from 1550 to 1750°C for 2 h with the compositions (Nd 0.18 Yb 0.18 /Nd 0.18 Y 0.18 )Si 10.36 Al 1.62 O 0.54 N 15.46 . The densification process, reaction sequence, cell dimensions and microstructure were studied in comparison with the corresponding single cation α-sialon. Experimental results have shown that the samples hot-pressed at 1750°C mainly consist of α-sialon phase, whose content (around 95 wt%) is higher than that of counterpart single rare earth doped α-sialon, especially much higher than the one of Nd-α-sialon. On the other hand, the multi-cation α-sialons compositions are beneficial to lower the eutectic temperature in the systems, thus promoting the dissolution of intergranular crystalline melilite phase, and facilitating the precipitation of α-sialon phase. TEM and EDS revealed that the amount of Yb 3+ or Y 3+ , which possess relatively smaller ionic radii than Nd 3+ , is higher than that of the Nd 3+ in α-sialon grains and more Nd 3+ are remained in the grain boundary phase. Small amount of elongated α-sialon grains were observed by TEM and the preferred orientation also occurred under hot-pressing for such a low x value composition ( x =0.36) used in this study.

A high-permittivity SrTiO3-based grain boundary barrier layer capacitor material single-fired under low temperature

A strontium titanate (SrTiO3)-based grain boundary barrier layer capacitor (GBBLC) dielectric material containing niobium pentoxide (Nb2O5), bismuth titania (Bi2O3·3TiO2) and lithium fluoride (LiF) has been produced by a single firing process below 1200 °C. Its dielectric properties and microstructure show typical values of eeff∼37×104, tangent δ∼4%, capacitance change with temperature ΔC/C<±3% in the range 20–150 °C and an average grain size of 5 μm. The mechanism by which Bi2O3·3TiO2 affects the barrier layer properties is also discussed.