Photonic crystals are a new type of artificial materials with multi-dimensionally periodic dielectric
structures. They can create a range of forbidden frequencies called photonic bandgap. Photons with energy lying in the gap cannot propagate through the
medium. This has the fascinating prospect to shape and mould the flow of light for photonic information technology, and thus makes photonic crystals
one of the hottest research fields nowadays. In this article the author will review the band structures, anticipated applications and preparation
methods of photonic crystals.

The paper made an overview of the classification, material design and the influences of nano-sized particles on the microstructure and properties of nanocomposite ceramics. Finally the author proposed that further improvement of the performances of the ceramics could be achieved by the hybridization of micro and nano composite and the control over the grain morphology.

This paper reviews the research process about machinable ceramics from three parts of glass-ceramics, oxide-ceramics and nonoxide-ceramics in detail, discusses its fabrication procedure and mechanism of machinability, and also gives some trends in this field of research.

The uniformity of PbWO₄ crystals grown by the Bridgman method was investigated by the measurements of transmission and light yield for full-size crystals and the different parts of ingot.The results show that the crystal quality in the later growth period is the main factor mfluencing the uniformity, and a favorable geometric shape can improve the uniformity of PbWO₄.

The dissolution process of the 25Na₂O-25CaO-50P₂O₅ glass with different initial surfaces
was analyzed with the help of the surface weight loss and the morphology of the glass surface. The experiment of weight loss of the glass shows that
the dissolution process of the glass has two stages. the first stage, diffusion stage, at which the weight loss of the glass is proportional
to the square root of the dissolution time; the second stage, linear dissolution stage, at which the weight loss of the glass is in direct
proportion to the dissolution time. During the dissolution process of the glass, The etched pit forming stage and the etched pit stable stage were
observed, and these two stages agree with the two stages of the weight loss. The results also demonstrate that the initial surface of the glass has
remarkable effect on the dissolution process of the glass.

The optical transitions intensity parameters of Er³⁺ in MFT glass were calculated by using the J-O theory. The transition
probabilities, branching ratios and lifetimes of Er³⁺ ion were obtained. The excitation spectra were measured monitored at intense
green of ²H_11/2, ⁴S_3/2→⁴I_15/2 transitions and red fluorescence of ⁴F_9/2→⁴I_15/2 transition
of Er³⁺ ion. The fluorescence intensity variation with temperature for ²H_11/2, ⁴S_3/2→⁴I_15/2 transitions was observed.
The fluorescence decay of ²H_11/2, ⁴S_3/2→⁴I_15/2 transitions was measured and the quantum efficiency and non-radiative transition rates were calculated.

Standard enthalpy change, free energy change, entropy change, the frontier orbital energy and relative
stability of free radicals about the 8 types of design pyrolysis processes of the series of m-xylene compounds were calculated by the AM1 method in
Gaussian 98 program package. The results show that the pyrolysis process of these compounds first starts from the C--H bonds of the methyls on the
benzene rings. This conclusion is in accord with the experimental result. The activity sequence of the series of m-xylene compounds is
C₈H₉OH(d₁)>C₈H₉SH(d₂)>C₈H₁₀(a)>C₈H₉-CN(d₃). At the same time, it is also proved that the frontier orbital energy difference
and the relative stability of these free radicals are the same as the thermodynamics parameters, so that they can be used to the study of the
pyrolysis mechanism and thermoreactive activity of this series of xylene compounds.

Phase transitions of Li₂O-Al₂O₃-SiO₂ based glass-ceramic materials, which can be used for the fabrication of optical fiber ferrule, were studied by
means of DTA, XRD, SEM and CTE. The temperature range of the phase transition studied was 850～1270℃. The results show that the metastable
β-quarts s.s first precipitates at 870℃ and translates into the β-spodumene s.s, the prominent crystal phase, at higher temperature. Increasing the heat-treatment temperatures from 900℃ to 1000℃ and prolonging
the time, the size of the granule changes little. With the transition of β-quarts s.s. to the　β-spodumene s.s, the CTE of the material increases greatly and
then it gradually stabilizes when the transition is completed. During the heat-treatment of the material at 1150～1270℃, the granule size grows and the glass
phase increases quickly. At the same time, the CTE of the material increases too.

The nanocrystal α-Fe₂O₃ with an average size of about 30nm was prepared by a sol-emulsify-gel method in
the iron nitrate and 2-methoxyethanol system. The powders were characterized by TEM, XRD and the xerogel primary powders thermal stability was studied by
TG-DTA. The gelation time was reduced greatly by adding tetrabutyl titanate. When tetraethyl orthosilicate instead of tetrabutyl titanate, the gelation
time can be much longer. γ-Fe₂O₃ with spinel structure appeared as the main phase in the calcinated powder and the average particle size
was about 10nm. A new idea to improve the gas sensitivity and stability of γ-Fe₂O₃ gas-sensitive materials was provided. The results show
that the introduction of surfactant(SDS) is helpful to form pure crystal phase α-Fe₂O₃.

By rheological experimental measurements of SnO₂ sol systems derived by the precursor
Tetrabutylorthostannate Sn(OBuⁿ)₄, it was reported that tear viscosity η, intrinsic viscosity [η] and pH values of the sol solution systems varied dynamically with time. Based on the rheologically dynamic observations, the growth character of SnO₂ sol
grains and its structural evolution rule were discussed, and proton H⁺ production phenomena associated with sol grain growth process were also explained. From
experimental investigations and theoretical discussion, the growth process of SnO_2 sol grains is controlled by a three-stage growth model,
and grain structure keeps invariant during the growth period before sol→gel transformation and sol solution acidity (pH)
influences profoundly the sol grain growth rates.

With carbon as an additive, the fracture toughness of Al₂O₃/TiC ceramic material fabricated by hot pressing technology is increased by 20% than that of
Al₂O₃/TiC composite without any carbon added. The results of theoretical and experimental analyses show that the existing of weak interfaces in the ceramic
material is one of the effective approaches to achieve higher fracture toughness. The added carbon, existing as a form of graphite, can result in not only the
formation of spontaneous microcracks but also the formation of weak interfaces. As a result of the comprehensive integration and synergism of varieties of single
toughening mechanisms such as crack bridging, crack branching and crack defection etc., the fracture toughness of Al₂O₃/TiC ceramic material can be enhanced obviously.

The 50Ti/HA biocomposite was fabricated by hot-pressing technique. The microstructure and in vitro bioactivity of the biocomposite were investigated.
The XRD results show that some reactions between titanium and hydroxyapatite occur in the biocomposite during sintering at 1200℃. The main reaction
products are Ti₂O, CaTiO₃, CaO and a TiP-like phase. A continuous hydroxyapatite film can be formed on the surface of the biocomposite when it is immersed in the
SBF for one day, and the thickness of the apatite film increases with the increase in immersion time. The apatite film has a preference along the orientation of [001]
and its formation is mainly due to the present of Ti₂O phase in the composite.

Tape casting process of aluminium nitride substrate was studied from the following aspects such as particle
size, the style of slurry fluid, drying condition and debinding mechanism. As a result, it was indicated that various particle size directly influenced the slurry viscosity and the amout of dispersant. The style of slurry fluid
suit for tape casting of AlN was pseudo plastic. The green tape with flat and smooth surface was fabricated when keeping solvent atmosphere.
Twice-debinding process was an available way to remove carbon impurity in the AlN green tape. The SEM photograph of the fractured surface of the
sintered substrate showed that crystal particle grew well, open porosity did not appear and fracture mode was intercrystalline fracture.

Alumina precursor-coated nanosized Ni powders were prepared by the heterogeneous precipitation
method in the aluminium salt solution. The chemical composition of the as-prepared coated powder was characterized by energy dispersive
spectra and Auger electron spectra. It revealed that nanosized Ni particles were homogeneously coated with layers of alumina hydrate.
The calcined powders that were performed in argon were hot pressed in a protective atmosphere of argon. The experimental results indicate
that the calcined powders can be sintered to nearly fully dense at a lower temperature as compared with that from sol-gel prepared powder
mixtures. The microstructures of these sintered specimens are different from that of ball-milled and hot-pressed counterparts. Irrespective of
the location of Ni particles in alumina matrix, there exist holes at the interfaces between alumina grains and Ni particles, which is attributed
to thermal expansion mismatch between alumina and nickel. The fracture mode of these composites is mainly an intergranular-type.

A series of AlN-borosilicate glass multiphase ceramics were produced by using SHS chemical oven on the
parabolic plane by which different gravity obtained. The influences of different gravity levels on material diffusion and its microstructure
during liquid phase sintering were discussed. The results show that the different phase segregation can occur under elevated gravity conditions. On the contrary,
the multiphase ceramics with uniform distribution of different phases and well growth of AlN grains can be obtained in microgravity. Therefore,
microgravity proves good conditions to fabricate improved materials.

The dense oxide layer is formed on the surface of sintered α-SiC after annealing at 1200℃ for 10h in a stationary air ambient, and its crystal
structure is of β-cristobalite. The growth of the oxide layer is controlled by the diffusion of oxygen molecules through the interstitial site in SiO₂. The solid state reaction between SiC and Fe is
severe, and significantly decreases the interface stability of SiC/Fe. The oxidation of SiC has a great effect on the interface stability of SiC/Fe. At temperatures below 900℃,
the interface of oxidized SiC/Fe is always smooth and remains intact after annealing for a long time. It shows that the oxide layer can hold back the interface reaction and
improve the interface stability, permanently. But, the interface stability of O-SiC/Fe decreases corresponding to raising the annealing temperature. The reaction first takes
place at the “points” of the interface, and then, wholly extends along the interface. It results that the effect of the oxide layer as a reaction barrier is lost entirely. The main
reasons for the oxide layer invalid after annealing at the temperature above 900℃ may be the voids existed in the oxide layer, and the stress concentration caused by the
mismatch of the heat expansion coefficients between the oxide layer and SiC, Fe.

A strategy for the systematic selection of perovskite-type mixed conducting membranes with high oxygen
permeability, phase stability and thermo-chemical stability was developed. Several promising membrane materials were then pointed out. Some of the
materials were synthesized by using standard ceramic method and complexing method, their oxygen permeability and stability were investigated and
compared with several typical conducting membranes such as SrCo_0.8Fe_0.2O_3-δ and SrCo_0.5FeO_3.25 etc. The results show that the new materials indeed possess the expected properties.
The permeability of a typical material, Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ membrane at 850℃ reaches 1.16mL[STP]·cm^-2·min^-1, higher than that of SrCo_0.8Fe_0.2O_3-δ
membrane under similar operation conditions, the permeation flux can keep stable more than 1000h’s operation.

Ellipsometric spectra of Ba_0.9Sr_0.1TiO₃ (BST) thin films with various annealing
temperatures were measured in the range of photon energy from 2.1 to 5.2eV. Constructing appropriate fitting models and describing optical properties
of the BST with Cauchy dispersion model, their optical constants (refractive index n and extinction coefficient k) spectra and band
gap E_g were determined by means of an optimization. Compared these results, we obtained the variation of the refractive index n,
the extinction coefficient k and the band gap E_g with annealing temperatures.

Mixed-conducting Sr₄Co_xFe_6-xO_13±δ oxides were synthesized by pyrolysis of cellulose-citric-metal salt compound.
Their crystal structures were investigated, and oxygen permeability of Sr₄Co₂Fe₄O_13±δ was also studied by a GC method. The
introduction of cobalt in Sr₄Fe₆O₁₃ led to the occurrence of perovskite phase in the Sr₄Fe₆O₁₃ bulk even at low doping
content of cobalt (x=0.5), some minor CoO phase was also observed when x=2.0, and the material mainly demonstrated perovskite structure when
x=2.6. The phase structure of Sr₄Co_xFe_6-xO_13±δ was found to be closely related with the calcined temperature and the
oxygen concentration in the ambient atmosphere during calcination or retreatment at high temperature. The air-synthesized sample had the
intergrowth phase Sr₄Fe_6-xCo_xO_13±δ and the perovskite phase Sr(Fe, Co)O_3-δ coexisted along with CoO impurity. The
N₂-annealed sample coexisted of Sr₄Fe₆O₁₃ phase, brownmillerite phase and minor CoO impuirty. When Sr₄Co₂Fe₄O_13±δ
was treated in pure oxygen environment, the sample changed to single phase (Sr₄Fe₆O₁₃ type phase). The oxygen permeability of
Sr₄Co₂Fe₄O_13±δ membrane had a value close to 1.5×10^-8mol/cm²·s at 1123K. From 923K to 1223K, the activation energy for oxygen transportation was about 70kJ/mol.

Cubic pyrochlore structure α phase and low symmetry structure β phase are the basic
phases of BZN-based ceramics. The α phase is a congruent compound, its congruent melting point is 1190℃, corresponding to negative
temperature coefficient of dielectric constant. The β phase is an incongruent compound, its incongruent melting point (peritectic temperature)
is 1100℃, corresponding to positive temperature coefficient. The zero temperature coefficient of CH grade would be met with fixed
α/β phase ratio. In this paper, dielectric properties of Ag-doped BZN-based α phase, β phase and CH grade diphasic ceramics were explored respectively. The results show the effects of Ag-dopant on the dielectric properties of BZN-based α phase,
β phase and CH grade diphasic ceramics. The melting behaviors of Ag-doped BZN-based β phase were explored too. The change of
incongruent melting point results in the change of the dielectric property of Ag-doped BZN-based ceramics.

The dielectric properties of PMN-BT solid solution ceramics were systematically studied. The change of the transition temperature
with composition is in the form of “U” curve and the possible cause may be existing of paraelectric phase Ba(Mg_1/3Nb_2/3)O₃
in PMN-BT ceramics. The effects of composition on dielectric relaxation for PMN-BT ceramics were studied. With increasing BT content,
dielectric relaxation of PMN-BT ceramics was increasing first, then decreasing. The characteristics of phase transition temperature of
the ferroelectric solution composed of two perovskite compound were also discussed.

The composite ceramics with PZN-based relaxor ferroelectrics were prepared by two-step process. The dielectric and electrostrictive properties of the composite ceramics were investigated. The results reveal that the temperature stability of the composite ceramics can be greatly improved. The composite ceramics have little hysteresis with high electrostrictive strains and excellent dielectric properties.

The effects of Cr₂O₃ addition on piezoelectric properties，microstructure and morphology of the domain of PZT-PMN ceramics
were studied by TEM, SEM, ESR and other conventional electrical methods. The measurement results of piezoelectric properties showed that the
Cr₂O₃ addition was effective in increasing the K_p and Q_m when its concentration was below 0.06wt%, which indicated
that Cr-doped PZTMN ceramics possessed the properties of “soft” and “hard” piezoelectrics simultaneously. Furthermore, the properties were
found to get “hard” with the increase of sintering temperature even for the ceramics with the same compositions. Electron Spin Resonance (ESR)
analysis showed that Cr ion coexisted in both Cr³⁺ and Cr⁵⁺, and the valence change from Cr⁵⁺ or Cr⁶⁺ to Cr³⁺ happened
when the sintering temperature was increased, which was believed to be one of the reasons for its hardness of the properties. TEM images
revealed that, with the increment in Cr content, the normal stripe-like domain changed to wavy domain due to the domain pinning by the defect
complexes of acceptor impurities and oxygen vacancies.

Three dimensional textile SiC/SiC composites were fabricated by chemical vapor infiltration, and
their mechanical properties and microstructure were investigated. The density of the composites was 2.5g·cm^-3 after the
preform was infiltrated for 30 hours. The present composite materials exhibited excellent mechanical properties and metal-like failure behavior.
The flexural strength and displacement were 860MPa and 1.2mm, respectively. Fracture toughness and work of fracture were 41.5MPa·m^1/2 and
28.1kJ·m^-2, respectively. The dynamic toughness was determined by using Charpy impact method and its value was 36.0kJ·m^-2.

Alpha alumina nanocrystalline powders, with mean particle size less than 50nm, were prepared by a novel synthesis process using Al(NH₃)₃·9H₂O and NH₃·H₂O solutions as raw materials. The process mainly utilized a seed-effect of fine grains worn from the milling mediums and also utilized ZnF₂ or AlF₃ additives. The phase transformation temperatures to alpha alumina can be reduced dramatically to 900-920℃ by improving the homogeneity of seeds with the hydrous alumina and accelerating the mass diffusivity and transportation in the transformation process.

The ultrafine CaCO₃ crystal growth controlled by Na₅P₃O₁₀ in the carbonation of Ca(OH)₂ suspension, was investigated by using SEM.
The results show that CaCO₃ nucleates along with the nucleus growth. The presence of Na₅P₃O₁₀ accelerates the CaCO₃ nucleation. At the
initial stage, a large number of CaCO₃ nucleus engender, and metastable tiny crystallites (R=23～26nm) can be observed in SEM imagine. The CaCO₃ crystal
growth controlled by short distance diffusion when mass pass through the crystal interface, does not correspond to Zener-Ham theory. At the next stage, the metastable
tiny crystallites disappear in SEM imagine. The CaCO₃ crystal growth abides by the long distance control model R(t)=λ_i(Dt)ⁿ, in which the time coefficient
n is 0.4874～0.4992 (theory value n=0.5) and the constant λ_i Dⁿ decreases from 16.69 to 11.36. Consequently, Na₅P₃O₁₀ can effectively inhabit the CaCO₃ crystal growth.

La_0.9Sr_0.1Ga_0.8Mg_0.2O_3-α was prepared by a citrate method. Thermal analysis (TG/DTA) was used to characterize the thermal decomposition of the organic ligands of the gel. The gel decomposed to its oxides at 256-309℃. X-ray diffraction patterns indicate a pure primitive-cubic phase is formed by 1300℃ without impure phases. The impedance spectra of an 88%-dense sample exhibit no grain-boundary contribution, a conductivity σ=2.l×10^-2Scm^-1 at 800℃ and an activity energy E=0.98eV.

The feasibility of fabricating AlN was demonstrated. The effects of additives and nitridation temperature on the behavior in direct nitridation of molten
Al-Si-Mg alloys were investigated. The experiments were carried out at different temperatures under high pure nitrogen atmosphere. The main role of additive elements,
and the nitridation process of molten aluminium alloys were also discussed on the base of thermodynamic analysis. Moreover, the effects of temperature and additives
in raw alloys on the nitridation rate were investigated by TG experiments.

The effects of ion implantation on the structure of nano-Si₃N₄ was studied by means of FT-IR, XPS and photoluminescence spectra. The energy level scheme and the energy structure of nano-Si₃N₄ were given. The results show that ion implantation makes free Si in the material change to SiN_n(n=l, 2), and nano-Si₃N₄ possesses a quantum confinement effect, and its photoluminescence peak position and intensity are unstable.

The visible-light absorption of rutile was raised through doping Cr ion into the surface of rutile crystal with high-temperature-diffusion-doping-sensitization technique. TiO₂:Cr
specimen was analyzed by means of UV-VIS, XFA, XRD, XPS and LRS, respectively. As a result, it is shown that after Cr ion is doped
into the surface of the crystal, Cr ion exists in the solid-melting-state Cr₂TiO₅, which induces the original absorption edge(410nm)
move to 750nm, and achieves match with solar spectrum and raises optical absorption to visible-light effectively.

Polycrystalline carbon nitride thin films were prepared on Si (100) by hot filament assisted rf plasma-enhanced chemical vapor deposition with negative bias methods. X-ray distraction (XRD) spectra indicate that the obtained CN films contain both crystalline β－C₃N₄ and β-C₃N₄, and a presently unknown structure. Some crystalline particles of 1-2μm in size with hexagonal cross section exist in the polycrystalline carbon nitride film. The maximum hardness of C₃N₄ thin film is 72.66GPa.

The transitional phase appeared when two ferroelectric powders with different Curie point were
mixed and sintered together. The characteristics of the transitional phase were related to the original phases. After
BaTiO₃ (BT) and Pb(Mg_1/3Nb_2/3)O₃ (PMN) were co-fired, the dramatic dielectric-temperature characteristics can be observed.
The results show a new phase with a lower Curie temperature (T_c) formed. The T_c of BT raises under the high ambient temperature,
which indicates the entrance of the Pb cation into the lattice of BT. The co-fired sample can be prepared with such excellent characteristics,
the dielectric constant is more than 3000 at room temperature, the dissipation factor is lower than 60 and the temperature coefficient of
capacitance (TCC) accords to the X7R standard.