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Herein we proposed an approach to quantitatively evaluate the individual contribution of orthorhombic and tetragonal phase in the polymorphic phase transition (PPT) region of Li modified (K,Na)NbO3 during the poling process. Through investigating the feature of domain switching in orthorhombic and tetragonal phase, it found that the essence for the switching of polarization vectors 〈110〉 in orthorhombic phase and 〈001〉 in tetragonal phase was tiny ion displacement. With the increase of Li content the volume ratio of tetragonal phase in the coexistence phase at room temperature went up as well as the value of ion displacement and X-ray diffraction results could clearly elaborate the validity of the above statement.

The temperature dependent properties of (K,Na)NbO3-based piezoelectric materials enlightened us that the combination of compositions gradient could remedy the fluctuation of the electrical properties induced by the temperature variation. Then Li modified (K,Na)NbO3 ceramics was chosen as target materials and a multi-layered structure containing a series of composition gradient layers was prepared via a conventional solid state reaction. The results of relative permittivity against temperature demonstrated that the as-called relaxor feature was observed in this proposed multi-layered structure and the change rate of the dielectric anomaly peak got evidently reduced. Besides, the field-induced strain varying less than 10% from the room temperature to 100 °C was also achieved in this layered-structure ceramics. Moreover, the investigation here could render us an important reference for designing ferroelectric materials to satisfy the diversified requirements in the functional device.

Rare earth doped perovskite oxides have attracted much attention due to their multifunctional properties (such as photoluminescence, ferro-/piezoelectricity and so forth). In the current work, Er3+-doped (Li,K,Na)NbO3 nano-ceramics were successfully synthesized by spark plasma sintering and as-obtained ceramics exhibited excellent up-conversion photoluminescence (UC PL) behavior. The influences of the doping of Er3+ on the phase structure, microstructure, and UC PL properties were systematically investigated. The XRD and Raman analysis demonstrated that Er3+ ion entered into A site of (Li,K,Na)NbO3 perovskite structure. The most obvious enhancement of UC PL emission was achieved in the ceramics with 0.25 mol% of Er3+ doped, and the intensity of UC PL emission dropped with the further increase of Er3+ doping. Moreover, it found that two photons contributed to this observed UC PL behavior. These findings here rendered potential application of Er3+ doped (Li,K,Na)NbO3 smart materials in novel multifunctional devices.

Multifunctional luminescent materials based on rare earth doped ferro-/piezoelectrics have attracted much attention due to their potential applications in novel multifunctional devices. Herein, we choose Li modified (K 0.49 Na 0.51 )NbO 3 system benefitting from both of the effect of morphotropic phase boundary and polymorphic phase transition as the target materials, and systematically studied the influence of the doping of Er 3+ on the phase structure, composition, up-conversion photoluminescence property and so forth. A significantly enhanced ferro-/piezoelectric behavior had been achieved in 0.5% Er 2 O 3 doped (Li,K,Na)NbO 3 ceramic. Our results reveal that in addition to the admirable intrinsic piezoelectric properties of (Li,K,Na)NbO 3 ceramic, the donor doping behavior of Er 3+ could enhance the ferro-/piezoelectric properties and obviously improve the up-conversion photoluminescence property of the matrix materials. These findings show great potential of Er 3+ doped (Li,K,Na)NbO 3 materials a future application in novel multifunctional devices.

Er 3+ doped (K 0.52 Na 0.48 ) 1− x Li x NbO 3 ceramics had been prepared through a conventional solid state reaction routine and their phase structure, ferroelectric, piezoelectric, and photoluminescence properties were systematically investigated. X-ray diffraction results clearly illustrated a phase transition from the orthorhombic to coexistence and further to tetragonal phase with the increase of Li content. Via measuring the ferroelectric and piezoelectric properties of the ceramics, it found that the polymorphic phase transition (PPT) effect contributed the obvious enhancement in electrical properties of the Er 3+ doped (K 0.52 Na 0.48 ) 0.94 Li 0.06 NbO 3 ceramic which lay in the composition region of coexistence phase structure. The up-conversion photoluminescence intensity of green emission and red emission first increased as x increase from 0 to 0.06 and then decreased for x = 0.08. The most obvious enhancement in the up-conversion photoluminescence intensity was also achieved in the composition lying in the vicinity of PPT region. And the above circumstance caused the consideration that here the essence of the coexistence phase may be a phase structure with lower crystal symmetry instead of just physical combination of orthorhombic and tetragonal phase.

The specific heat (CP), thermal diffusivity (η), thermal conductivity (κ), magnetization, resistivity (ρ), and magnetocaloric effect (MCE) were studied in fast-quenched ribbon samples of the Ni50Mn37-xAlxSn13 alloy (x = 2, 4). Anomalies are observed in the form of a jump for the temperature-dependent η(T) and κ(T) near the magnetic and magnetostructural phase transitions, which are associated with critical scattering of heat carriers by distortions of the crystal structure, fluctuations of the order parameter, or structural/magnetic inhomogeneities. The transition to the martensitic phase is found to be accompanied by a sharp increase in the resistivity, suggesting an increase in the electron relaxation rate due to structural distortions inherent in martensite. The value of the magnetoresistive effect at 1.8 T near the martensitic transition reaches ∼40%. The temperature hysteresis was investigated in terms of ρ(T) near TC, which is explained based on the coexistence of the magnetic two-phase state of FM + AFM and the structural magnetic heterogeneity of the samples with dominant austenitic phase. For a sample with x = 2, the electron and phonon components of thermal conductivity were estimated (κph » κe).

The flower-like Co 3 O 4 assembled with nano-leaves could be obtained through annealing the cobalt hydroxide carbonate precursor, which was first synthesized via one-pot hydrothermal route. X-ray diffraction and TEM analysis demonstrated the transition from the precursor of amorphous state to Co 3 O 4 with cubic phase structure. XRD results indicated the increase in the calcination temperature from 300 to 400 °C for the precursor would bring about the increase in the crystallinity degree and ferromagnetic property of the products. The TG analysis demonstrated that as prepared Co 3 O 4 samples for different calcination temperature had significant effect on the thermal decomposition of ammonium perchlorate. And the decomposition temperature region of ammonium perchlorate could be decreased from 303–454 °C to 256–356 °C by the catalysis of Co 3 O 4 .

Er 2 O 3 doped (K,Na)NbO 3 (KNN) ceramics with the composition around the morphotropic phase boundary was synthesized by the conventional solid state reaction. Compared to pure KNN ceramics, KNN doped Er 3+ ceramics exhibited enhanced ferroelectric, piezoelectric properties owing to the donor doping effect. And the maximum value of d 33 =132 pC/N and k p=0.44 were obtained for the ceramics with the addition of 0.5 mol% Er 2 O 3 . Meantime, the intensity of absorb spectra and photoluminescence were obviously enhanced in this kind of sample owing to the lattice distortion induced by the polarization reorientation during poling process. The present work indicated the proposed system exhibited potential application in multifunctional integration device.

Microsphere, micro-net-sphere, hexagon plate and sandwich-like cobalt particle were successfully synthesized via a facile, environmentally friendly and one-step solvothermal method. Subtle control over the reaction conditions could easily achieve these different morphologies with certain crystal structures. Solvothermal method utilized here is pollution free, without surface-active agent and facile to perform. The effects of alkali and Co 2+ content as well as the reaction temperature on the size, morphology and microstructure were investigated individually. Moreover, the catalytic properties concerning the catalytic thermal decomposition of ammonium perchlorate (AP) and magnetic properties of these selected samples were evaluated. It finds that the alteration trend of related properties correspond well with the variation of these samples’ microstructure and morphology. In addition, comparing with the other morphology, Co particles with the morphology of hexagon sheet exhibits outstanding catalytic performance, implying significant practical application in the development of energy-efficient rocket solid propellant recipes.

The influence of sintering temperature and poling processing on the room temperature phase structure and piezoelectric properties of Li0.058(Na0.51K0.49)0.942NbO3 ceramics were systematically investigated. An approach was proposed to roughly determine the ratio of tetragonal and orthorhombic phase in the as-sintered samples. The result of temperature dependence of the dielectric constant proves this method feasible. The best piezoelectric properties of d33 = 255 pC/N was obtained in specimens sintered at 1040 °C. The dense microstructure and high percentage of 90° domains reorientation during poling processing could explain the best performance of samples for 1040 °C. The loose microstructure and low density for the samples of 980 and 1080 °C are responsible for the worse piezoelectric properties comparing with that of sample for 1040 °C. Meanwhile, the segregation also plays an important role in the deteriorate properties for the sample sintered at 1080 °C.

Several kinds of phase structure change behavior in Li 0.058 (Na 0.51 K 0.49 ) 0.942 NbO 3 (KNNLN) ceramics were presented in this work. XPS measurement was employed to determine Na volatilization in the KNNLN samples, and this result explains the difference of the phase structure between the surface and interior of the samples. The phase structure of lead-free KNNLN piezoceramics are studied based on the measurements of the analysis of X-ray diffraction pattern and dielectric properties. The poled samples exhibit orthorhombic structure whereas the surface and interior for unpoled samples exhibit tetragonal and tetragonal-orthorhombic coexistent structures, respectively. An explanation to the mechanism of the structure transformation during poling processing was proposed.

Zr doped Ba0.6Sr0.4TiO3 ceramic was sintered by spark plasma sintering (SPS) and thermal treatment. Sintering behavior, microstructure and dielectric properties of the BST ceramics were investigated by XRD, SEM and impedance analyzer. High dense Ba0.6Sr0.4(Zr0.2Ti0.8)O3 ceramic with 98.2% of the theoretical density was fabricated at 1270 °C for 5 min. The dielectric constant of this sample reduced to 850 at 100 kHz, the tunability of the ceramic increased to 57% (1.5 kV/mm, 298 K) and the figure of merit (FOM) value increased to 475, which is promising material for tunable devices application.

The phase structure of lead-free Li 0.058 (Na 0.51 K 0.49 ) 0.942 NbO 3 (KNNLN) ceramics can be affected by the stress as well as the external electric field. A high piezoelectric constant was obtained in KNNLN ceramics by adjusting the cooling-down speed of the sintering. The {2 0 0} reflection X-ray diffraction lines were measured to accurately identify the room-temperature crystal structure of the as-sintered samples. Dielectric measurements were performed to observe the differences in the phase structure of KNNLN ceramics before and after poling.

Plate-like Bi 5 Nb 3 O 15 (B5N3) particles and rectangular KNb 5 Bi 2 O 16 (KN5B2) particles were synthesized by the molten salt process and topochemical microcrystal conversion (TMC), respectively. The effects of the synthesis parameters on the phase structure and morphology of B5N3 precursor and KN5B2 were investigated. Results indicated that the retro-synthesis process of the as-synthesized KN5B2 retained the morphology and structural feature of the B5N3 precursor. The prepared KN5B2 particles with high aspect ratio of 20–30 are promising templates for texturing bismuth-layer and alkali niobate based ceramics by (reactive) templated grain growth method. The same method can be applied to other perovskite-structured templates.

By coupling strong and weak exothermic reactions, (TiC + SiC) composite powders have been prepared by combustion synthesis. The reaction temperature and heating rate strongly depend on the Ti/Si ratios in the reactant powder mixture. The phase assemblage and microstructure of the products can be manipulated by varying the starting compositions. According to SEM observation, the reaction procedure and formation mechanism of TiC and SiC are discussed. It is proposed that the presence of metallic melt phases is important for the formation of the carbide phases.

Co-doped ceria electrolytes of Ce 0.8 Gd 0.2− x Y x O 1.9 ( x = 0.0–0.20) fine powders were prepared with glycine–nitrate method. The results of X-ray diffraction showed that all powders crystallite calcined at 873 K were single phase with cubic fluorite structure. The average crystallite sizes calculated by the Scherrer formula were between 21 and 23 nm, which was in good agreement with the results of TEM and particle size distribution measurements. The thermal expansion curves of Ce 0.8 Gd 0.2− x Y x O 1.9 were measured and the thermal expansion coefficients between 373 and 1123 K were calculated. The SEM results exhibited that electrolyte pellets sintered at 1523 K were dense, and the relative densities of these pellets were over 96%. The impedance spectra analysis of these electrolytes has been performed at 623–1023 K. The results showed that co-doped ceria exhibited higher ionic conductivity and lower activation energy than the singly doped ceria with the same dopant concentration at the temperature range of 773–1023 K, and the electrolytic domain boundary of co-doped ceria was smaller than that of singly doped ceria at 873–973 K. It suggested that co-doping with appropriate ratio gadolinium and yttrium could further improve the electrochemical performance of ceria-based electrolytes. These co-doped samples are ideal electrolyte materials of intermediate temperature solid oxide fuel cells.

Co-doped ceria of Ce{sub 1-x}Gd{sub x-y}Y{sub y}O{sub 2-0.5x}, wherein x = 0.15 and 0.2, 0 {

α-SiAlON powders consisting of one-dimensional rod-like microcrystals were prepared by combustion synthesis in large scales. No obvious negative effect on reaction products was noticed by the increase of sample size, and α-SiAlON was synthesized as predominant phase in all the samples, even in CS-CL with the weight of 1000 g. These results showed good repeatability of combustion synthesis and its great potential in industrial production of α-SiAlON powders in large quantities. According to the phase composition of intermediate product, the reaction procedure in combustion synthesis of Ca α-SiAlON was proposed. At the same time, the strong influence of different starting compositions on the grain morphology of Yb α-SiAlON products was explained with the consideration of reaction temperature and grain growth character.

Bi0.5(Na0.8 K0.2)0.5TiO3 (abbreviated as BNKT) piezoelectric ceramics with extensive texture were prepared by the reactive templated grain growth (RTGG), using plate-like Bi4Ti3O12 (BiT) particles as the templates. Through the analysis of X-ray diffraction pattern of the obtained materials, extensive crystallographic texture was evaluated with a relatively high Lotgering factor (f ≥ 0.9), and the incorporated (Bi0.5 K0.5)TiO3 diffused into the (Bi0.5Na0.5)TiO3 lattice to form a single solid solution. The scanning electron microscopy showed that the in-situ reaction started at the vicinity of BiT surface and proceeded with heat treatment time toward the inner part of the BiT. The high textured BNKT piezoelectric ceramics demonstrated good piezoelectric performance without decreasing the depolarization temperature when they were sintered at 1200 °C for 10 h.

Consolidated Ca α-SiAlON ceramics with gradually varying microstructure and property was prepared by hot-forging. The shape deformation as well as texture development of the sample during forging was studied in detail. It was found that the forging process promoted the growth of elongated α-SiAlON grains and enhanced their preferred orientation with the longitude perpendicular to the pressing force. The strong texture offered the hot-forged sample an increased fracture toughness of 7.9 MPa m 1/2 , which was primarily attributed to the pull-out and debonding behaviors of elongated grains.

Al-27 and Si-29 solid-state NMR spectra and X-ray diffraction (XRD) patterns were obtained for alpha-SiA1ON powders prepared by combustion synthesis, according to which the phase transformation and structure evolution of ot-SiAlON were studied. It was found that in alpha-SiA1ON Si-29 chemical shift values (-48 < delta(Si) < -47) were close to those in beta-Si3N4 and alpha-Si3N4, indicating that Si atoms kept SiN4 coordination to a large extent in alpha-SiA1ON despite the presence of 0 atoms. Dissimilarly, Al-27 chemical shift values in alpha-SiA1ON deviated clearly from that corresponding to AlN4 coordination (delta(Al) similar to 112) and occurred in a range from 3Al 95.5 to 99.9, which should be assigned to tetrahedral AIQN4-, (0 < x < 4) coordination. The broadening effect of AlOxN4-x, peaks was noticed, which was suggested to induced by slight dispersion of alpha-SiAlON compositions. 27 Al resonances assigned to AlO4 or AlO6 were also observed, revealing the existence of glassy phase in combustion products. By comparing the intensities of AlO4 and AlO6 resonance peaks, it was found that the composition and structure of the co-existing liquid assisting alpha-SiAlON formation were not constant but varied with temperature in combustion synthesis. In addition, with CaF, used as Ca-source alpha-SiAlON with low oxygen contents (n < m/2) were prepared, and it was found that there was a low threshold of oxygen content only beyond which alpha-SiAlON could be formed. (c) 2006 Elsevier B.V. All rights reserved.

The equilibrium compositions of a thermite reaction system (Fe2O3+Cr2O3+CrO3+NiO+O2+N2+TiO2+C+S+CaO+Al), which was used to prepare Ni-based alloys, were predicted by means of the free energy minimization method. The effects of the reactant contents on the equilibrium compositions and the adiabatic temperature of the thermite reaction system were analyzed. The microstructure of the Ni-based alloys was investigated. The thermodynamic analysis indicated that the products of the thermite reaction system contained primarily Al2O3, Fe, Ni, Cr, Ni3Al and NiAl, due to impurities C, N2 and S in the raw materials, there could also exist TiC, Cr7C3, CrN, CaS and TiN in the equilibrium products. The amount of Ni3Al and NiAl in the products increased with increase of the aluminum content in the starting materials. The microstructure investigation showed that the Ni-based alloys consisted of austenite, ferrite, Ni3Al and NiAl. The existence of Ni3Al and NiAl in the Ni-based alloys reconciled with the predictions of thermodynamic analysis, suggesting the free energy minimization method is useful in designing advanced materials with multiple components by thermite reaction technique.

With the assistance of mechanical activation, yttrium-stabilized a-SiAlON was prepared by combustion synthesis in air, instead of high-pressure N2 atmosphere for the first time. The reaction activity of metallic particles was remarkably enhanced by mechanical activation, which conduced the reduction of grain size, increased the total surface area and formation of fresh surface. The formation of a-SiAlON by combustion synthesis in air was explained by a kinetically induced reaction mechanism, in which both initial formation of a-SiAlON and following avoidance of oxidation were fulfilled by the retardation of O2infiltration owing to the short reaction period and fast cooling rate. # 2006 Elsevier Ltd. All rights reserved.

(Nd,Dy)-containing SiAlON powders were prepared by combustion synthesis, where it was proved that the phase assemblage and grain morphology of final products could be tailored by controlling the relative contents of the two rare-earth elements. When the molar ratio of Dy/(Nd + Dy) was increased, the phase content of α-SiAlON was promoted and β-SiAlON was reduced. At the same time, the grain morphology of combustion products varied from elongated prismatic crystals to fine isotropic grains. It was also found that the lattice parameters of both α- and β-SiAlON were affected by Dy/(Nd + Dy) ratios. The experimental results were discussed by considering the different ability of Dy 3+ and Nd 3+ to stabilize α-SiAlON structure.

In Ti–Al–C system two ternary carbides of Ti 2 AlC and Ti 3 AlC 2 were prepared by combustion synthesis. Laminated grain morphology and a terraced structure consisting of several parallel laminated layers were observed. On the basis of SEM and TEM results, a layered growth mechanism was proposed to describe the formation of the terraced structure. In this mechanism, the ternary carbide grains will undergo a preferential growth, i.e. each layer grows fast and expands quickly in the basal plane and all the layers are successively stacked along the normal direction identical to the c -axis in the hexagonal structure. This preferential growth characterized by the terraced structure was widely observed in this study and hence may be a common behavior during the growth of Ti 2 AlC and Ti 3 AlC 2 crystals in combustion synthesis.

Novel β-SiAlON micropalings consisting of nanorods have been prepared by combustion synthesis with proper additives. According to TEM images associated with SAD pattern, the preferred growth direction of the nanorods is proved to be [0 0 1]. An epitaxial nucleation and anisotropic growth mechanism is proposed to explain the formation of those micropalings. By this mechanism, new fine crystals are formed on the side faces of coarse crystals and each coarse prismatic β-SiAlON crystal is surrounded by parallel nanorods.

Yttrium-stabilized α-SiAlON powders with rod-like crystals were fabricated by combustion synthesis. Effects of starting compositions including relative content of diluents on final phase assemblage and grain morphology of combustion products were discussed. With appropriate proportions of α-SiAlON seeds and NH4F additive, α-SiAlON powders with rod-like crystals could be fabricated. It was found that the addition of α-SiAlON and NH4F could improve the anisotropic growth of rod-like crystals. However, if too much NH4F was added, the phase purity of combustion products would be decreased obviously and more β-SiAlON was produced. Additionally, the as-synthesized α-SiAlON powders were heat treated at 1800 °C for 1 h to examine their stability at the elevated temperature. The experimental results showed that after the heat treatment, single-phase α-SiAlON was obtained, revealing the high stability of combustion synthesized α-SiAlON powders.

Yttrium- and ytterbium-stabilized α-SiAlON powders consisting of rod-like microcrystals were prepared by combustion synthesis. A quenching method was used to investigate the phase formation and microstructure evolution during the combustion synthesis of α-SiAlON. Three reaction stages were proposed for the formation of α-SiAlON as follows: nitridation of metal powders, formation of the co-existing liquid phase, and precipitation of α-SiAlON with the dissolution of nitrides. Different nucleation and growth modes of rod-like α-SiAlON crystals were observed: crystallization from liquid phase, or nucleation and growth based on the surface of as-existed large crystals.

In this paper, (Ca + Yb)- and (Ca + Sr)-stabilized α-SiAlON powders were fabricated by combustion synthesis. The influence of Ca 2+ incorporation on the phase composition and grain morphology of combustion products was discussed. The experimental results showed that with the incorporation of Ca 2+ well-developed rod-like (Ca + Yb) α-SiAlON crystals could be produced. It was also found that, when only Sr 2+ was used as stabilizing cation, the reaction product was (α + β)-SiAlON composite, in which β-SiAlON was the predominant phase and the relative content of α-SiAlON was low. With the incorporation of Ca 2+ , however, both the relative content and the lattice parameters of α-SiAlON were clearly increased. These results indicated that the incorporation of Ca 2+ could assist Sr 2+ into the α-SiAlON lattice structure.

Single-phase Yb α-SiAlON ceramics in-situ toughened by elongated grains were prepared by pressureless sintering, with the crystalline powder prepared by combustion synthesis used as seed crystals. The effects of seed addition on the densification, phase transformation, microstructure development, and mechanical properties of the samples were investigated in detail. From the experimental results, it was found that the added seed crystals could promote the phase transformation and facilitate the growth of elongated grains. By adding seed crystals the fracture toughness of the sintered α-SiAlON ceramics was considerably improved, with no obvious degradation in the bulk density and hardness at the same time.

By combustion synthesis, Y (α + β)-SiAlON ceramic powders consisting of rod-like crystals were prepared. Effect of starting composition on the phase assemblage of combustion products was studied. It was found that with the increase of oxygen content, the phase assemblage of products varied from single-phase α-SiAlON to β-SiAlON gradually. Novel β-SiAlON whiskers were also observed in the combustion products. From the whisker morphology, it was suggested that both VLS and VS mechanisms operated here. It was also noticed that the whiskers could nucleate either on the basal face or on the side faces of as-existed prismatic rod-like crystals.

By applying SPS technique, new Yb α-SiAlON ceramics in situ toughened by rod-like grains were prepared at a relatively low temperature of 1600 °C, with combustion synthesized seed crystals added. The effects of sintering temperature, heating rate, and the addition of seed crystals on the densification process, phase transformation, microstructure development, and mechanical properties of the samples were discussed in detail. The experimental results showed that Yb α-SiAlON ceramics could be almost fully densified quickly by SPS, and the fast heating rate was helpful to reduce the amount of intermediate phases. Higher sintering temperature and appropriate holding time were beneficial to the promotion of phase transformation and grain growth. It was also demonstrated that the added seed crystals played an important role in enhancing the phase transformation and facilitating the growth of rod-like grains. Being toughened by the rod-like grains via the mechanisms such as grain pull-out and debonding, the fracture toughness of as-sintered Yb α-SiAlON ceramics with additive seed crystals was remarkably improved.

Novel Y α-SiAlON whiskers with high aspect ratios were prepared by combustion synthesis, except for common isotropic grains. The growth process of whiskers was investigated, and experimental results showed that the predominant growth mode of whiskers was the vapor–liquid–solid (VLS) mechanism. In contrast to the usual situation, here the liquid phase played two roles during the growth of Y α-SiAlON whiskers; that is to say, in addition to acting as a medium for mass transportation, the liquid phase took part in reactions itself. It was also found that proper addition of Fe2O3 could facilitate the development of whiskers with no remarkable deterioration on the phase assemblage of combustion products.

In this paper, single-phase Yb α-SiAlON powder with rod-like crystals was fabricated by combustion synthesis. The microstructural development of the rod-like α-SiAlON crystals was studied, and anisotropic grain growth was observed. Furthermore, the growth mechanism of the rod-like α-SiAlON crystals was investigated, and the experimental results indicated that during the anisotropic grain growth, the fast growth plane was the basal plane in the hexagonal crystal lattice.

Cordierite-based ceramics were developed by sintering a glass selected from MgO-Al{sub 2}O{sub 3}-SiO{sub 2} system with an aim to use the material as high frequency chip inductors. A small amount of B{sub 2}O{sub 3} and P{sub 2}O{sub 5} were added to optimize the preparation conditions. The glass powder and sintered bodies were characterized by different analytical techniques such as TG-DTA analysis, X-ray diffraction, transmission and scanning electron microscopy. Pellets uniaxially pressed from the glass power could be sintered well at 950 deg. C having a density of above 99% theoretically, dielectric constant of 5.5, dielectric loss of 0.001 and thermal expansion coefficient of 26.7x10{sup -7} deg. C{sup -1} (20-400 deg. C). Crystalline phases in this sintered sample are predominantly {alpha}-cordierite (hexagonal high cordierite) and trace amount of {mu}-cordierite. SEM depicted a uniformly dense microstructure with crystals of granular habit in the sintered sample.

AlN ceramics without sintering aids were fabricated by spark plasma sintering (SPS). The as-received sample sintered at 1600 °C has a relative density up to 99.5%, which indicates a very high densification by this method. Microstructure observation by SEM shows that the grains have a very small size. The thermal conductivity of sintered AlN was measured using laser flash method and the effect of microstructure on the thermal conductivity was discussed based on the phonon scattering mechanism. The result shows that the very small grains limit the increase of the thermal conductivity of AlN ceramics densified by SPS.

The thermal conductivity and microstructure of Si3N4 ceramics used for power electronic substrate were studied in present paper. Thermal conductivity of Si3N4 ceramics sintered at different temperatures varied greatly. The microstructure of the specimens was studied with X-ray diffraction, EDS and transmission electronic microscope to reveal the difference in thermal conductivity. The experimental results showed that microstructure of Si3N4 ceramics sintered at different temperatures had different components in their grain phase and grain boundary phase, while electrical properties showed not much difference with different sintering temperatures.

The microstructure of sol–gel derived cordierite doped B2O3 and P2O5 was investigated in this study. This kind of material had a low dielectric constant, low dissipation factor and can be co-fired with high conductivity metals such as Au, Ag/Pd, Cu paste at low temperature (below 1000 °C), suggesting that it would be a promising material for high-frequency MLCIs. This paper focused on the crystallizing process from MASBP glass phase including crystallizing temperature, the size and morphology of the crystals and the growth direction of a bar crystal. The experimental results showed that crystallizing phases were α-cordierite and the growth direction of a bar crystal was about [−6 9 −3 0], by a 14° angle with an axis.

A process for manufacturing a directly bonded aluminum/alumina (DBA) power electronic substrate was developed in the present work. The bonding interface of the substrate was studied using transmission electron microscopy to elucidate the bonding mechanism of aluminum to alumina. The bonding strength, the wetting ability, the wire bonding capacity, the break down voltage and the thermal resistance of the DBA substrate were studied in comparison with those of a widely used directly bonded copper/alumina substrate. The results show that the DBA substrate has an excellent thermal cycle tolerance, and it is most suitable for assembling power electronic devices that are used under severe condition such as in vehicles.

Mechanical properties, microstructures and distribution of elements in the microstructures of aluminum alloys vacuum-brazed joints brazed with La and Ce doped Al–Si based filler metals were studied. The results showed that tensile strength could be increased to 288 MPa for LD30 vacuum brazed joint and 280 MPa for LD2 vacuum brazed joint, these strengths are more than 95% of base metals and higher than that of aluminum alloy joints brazed with non-rare-earth element doped filler metals like AlMgSi and AlSiCuMg. La and Ce are thought to have improved: (1) the wettability of Al–Si based filler metals, (2) the vacuum brazed seam’s quality and impurities’ distribution that is superior with the rare earth brazing content, and (3) the uniformity of the distribution of these elements in both the base metal and the filler metal.

In the present work, the dependence of microstructure and electrical properties on B-site non-stoichiometry (excess) for (Na0.474K0.474Li0.052)(Nb0.948Sb0.052)O3 − xTa2O5 (KNLNSTx) was symmetrically investigated. The phase structure was pure perovskite when x 0.02 mol, a secondary phase would be found in the samples. The results indicate that the densification and piezoelectricity were promoted as x < 0.01 mol. It is supposed that the low amount of Ta could induce A-site vacancy and favor the poling efficiency. KNLNSTx ceramics with x = 0.005 mol Ta2O5 have optimum electrical properties: d33 = 253 pC/N, kp = 0.437, Qm = 43 and tanδ = 0.027.

The oxidation of AlN powder added by the fluorides at temperatures below 700°C in air was discovered in this study. The obvious onset of oxidation of AlN with cryolite and YF3 additions is below 700°C with the product of α-Al2O3 phase, which usually occurs in single AlN powder above 1100°C. The changes on the weight and the FTIR spectra of the AlN powder fired at temperatures lower than 700°C show that cryolite and YF3 greatly promote the oxidation of AlN powder at these temperatures. Different from the action of cryolite and YF3 powder, CaF2 has no obvious effect on the oxidation of AlN. A possible oxidation process, in part corroborated by FTIR and XRF, was proposed to explain the results in the experiments. The oxidation kinetics of AlN in the presence of cryolite were also discussed at the temperatures ranging from 550 to 700°C from the data of the weight gains in this region. The result shows that the oxidation follows a linear law, which implies a reaction rate-controlled process. The considerably low activation energy of 67 kJ mol−1, which is associated with the quick oxidation and the formation of α-Al2O3 at temperatures below 700°C, was determined from the slope of the line fit.

In this work, the thermal conductivity of Si 3 N 4 ceramics sintered with 5 wt.% Y 2 O 3 and different amounts of MgO as additives at different temperatures was studied. Mg 5 Y 6 Si 5 O 24 was detected by X-ray diffraction (XRD) and experimental results showed that the amount of Mg 5 Y 6 Si 5 O 24 and the thermal conductivity of Si 3 N 4 ceramics were affected by both the sintering temperature and the amount of MgO. The relationship between Mg 5 Y 6 Si 5 O 24 and the thermal conductivity of Si 3 N 4 ceramics was discussed.

In this work, by the die-casting–bonding process at 948–1098 K and under N2 atmosphere, Al/AlN substrates is produced successfully. The bonding strength of Al and AlN substrate, which is more than 15.56 MPa, is tested by a mechanic testing equipment. The microstructure of the performance of the Al/AlN substrates is investigated by SEM and optical microscope. There is no reaction product in the interface of Al/AlN; the crystal of aluminium grow directly on the surface of AlN.

The fabrication of rodlike Ca α-sialon crystals through a combustion synthesis process is reported in this paper. The main morphological features in the product included rodlike crystals, two dimensional elongated platelets, and equiaxed particles. By proper adjustment of the combustion parameters, a high productivity of rodlike Ca α-sialon crystals in the final product could be achieved. The combustion reaction mechanism and the relationship between the combustion parameters and the particle morphology were investigated.

A reheating process was developed to improve the thermal conductivity of low-temperature sintered aluminum nitride ceramics with Dy 2 O 3 , Li 2 O and CaO as additives. After the period of reheating, the amount of secondary phase was reduced to a very low level through carbothermal reduction. Microstructural investigation showed that the better the microstructure, the higher the thermal conductivity.

The crystal structures and giant magnetoresistance of CaF 2 -doped La 2/3 Ca 1/3 MnO 3 compounds are investigated by means of X-ray powder diffraction (XRD) and magnetic measurements. The Rietveld powder diffraction profile fitting technique is employed to refine the crystal structures. The results indicate that the space group of all these compounds is Pbnm , with Z =4. In each unit cell, the 4a, 4c, 4c, and 8d crystal positions are occupied by Mn ions, La ions, O I , and O II anions, respectively. The F atoms substitute for the O atoms in the 8d crystal position. The Curie temperatures of these compounds are enhanced slightly by adding CaF 2 , and the giant magnetoresistance (GMR) ratios are higher than 67.6% in an applied field of 5 T.

Aluminium nitride (AlN) with various morphologies was fabricated through a sublimation-recrystallization method. The influences of type of reactor and temperature gradient were explored, as well as the orientations and growth mechanism of the obtained AlN whiskers. In the early stage of preparation, a vapour-liquid-solid (VLS) mechanism dominated, producing AlN pillars, whiskers and noncrystalline fibres. In the later stage, as the catalyst liquid was removed by volatilization, the pillars and noncrystalline fibres stopped growing, but the growth of AlN whiskers continued through a vapour-solid (VS) mechanism. By Laue method and rotating-crystal method of x-ray diffraction, together with electron diffraction, most of the AlN whiskers were discovered to grow on planes \(\left\{ {2\bar 1\bar 10} \right\},\left\{ {0001} \right\} \), or \(\left\{ {10\bar 1|} \right\} \), where l = 0, 1, 2, 3, along crystal axes \(\left\{ {2\bar 1\bar 10} \right\},\left\{ {0001} \right\}\), or \(\left[ {10\bar 1w} \right] \), where w = 0, 1, 2, 3. Oblique grown whiskers also appeared, with a growth direction at an angle of about 54° to the growth plane, \(\left\langle {10\bar 12} \right\rangle \).

The growth mechanism and morphologies of AlN whiskers prepared by the carbothermal reduction method are studied as well as the technological condition. All experiments were carried out in a vertical, controlled-atmosphere, graphite element resistance furnace. The reactor chamber volume is Φ250×210 mm, and the reactant weight is about 20 g each times (it contains about 70 wt.% Al2O3). Nitrogen pressure in the furnace is 0.1 MPa (1 atm). The optimum growth condition is at 1700°C for 5 h with flowing nitrogen (0.6 l min−1), when the raw materials are α-Al2O3 and graphite (Al2O3:C=4:1 in weight). The yield of AlN whiskers is about 3–5 g each time, and 50 wt.% or more of Al2O3 can convert to AlN whiskers. Generally, whiskers with hexagonal cross section grow along 〈0001〉 and plate-like whiskers have a growth orientation parallel to 〈01 1 1〉 et al other than 〈0001〉. During the growth of whiskers, the VLS mechanism and VS mechanism serve the function together. In the early stage, α-Al2O3 will react with CaO to form Ca-aluminates such as CaO·6Al2O3(CA6), CaO·2Al2O3(CA2), CaO·Al2O3 (CA). These Ca-aluminates can provide liquid catalysts for the nucleation of AlN whiskers. After that, the AlN whiskers will grow out from the substrate surface by the VS mechanism. As proximity to substrate surface, there is less growth space and higher supersaturation, and far from substrate surface, there is large growth space and low supersaturation. So near the substrate surface AlN whiskers are small and with irregular shape. Far from the substrate surface, AlN whiskers are sensibly straight and with regular shape.

Aluminum nitride (AIN) ceramics, with binary additives B2O3-Y2O3, were sintered at temperatures from 1700 to 1850 °C. The microstructure and sintering characteristics were studied by XRD, HREM, SEM and TEM/EDS, which showed that Y2O3 gave different yttrium aluminates through the reaction with Al2O3 under different conditions. With the increase of sintering temperature, the yttrium-to-aluminum atomic ratio Y/Al decreased in the secondary phases of the sintered bodies. It was discovered that B2O3 could dissolve in the yttrium aluminates, forming some ordered structure with a superlattice. After sintering at 1850 °C for 4 h, a specimen with a fine microstructure and a thermal conductivity of 190 W m−1 K−1 was obtained.