Youhua Yu

Effects of A-Site (NaCe) Substitution with Na-Deficiency on Structures and Properties of CaBi4Ti4O15-Based High-Curie-Temperature Ceramics

Three kinds of bismuth-layer-structured ferroelectric (BLSF) ceramics, CaBi4Ti4O15 (CBT), Ca0.8(CeNa)0.1Bi4Ti4O15 (CNBT), and Na-deficient Ca0.8(Ce0.1Na0.05\Box0.05)Bi4Ti4O15 [CN\BoxBT] (where \Box represents vacancies) were prepared by a conventional ceramic technique. X-ray powder diffraction showed that their crystal structures are a single phase of BLSF with m=4. Sintering characteristics of the three ceramics were also discussed. Scanning electron microscope (SEM) micrographs of CN\BoxBT showed that the grain is platelike. The A-site (NaCe) substitution can improve the piezoelectric constant d33 and high-temperature resistivity with decreasing Curie temperature. The modification by A-site (NaCe) substitution with Na-deficiency is more pronounced than CNBT, which not only leads to a very high piezoelectric constant d33 and high-temperature resistivity but also increases the Curie temperature. The reason for the high Tc (Tc=866°C) of CN\BoxBT is considered to be internal stress. As a result, Na-deficient CN\BoxBT ceramic is found to be an excellent high-temperature piezoelectric material.

Influence of sintering temperature on the properties of high Tc bismuth layer structure ceramics

Abstract Bismuth layer structure Ca 0.82 (NaCe) 0.09 Bi 4 Ti 4 O 15 piezoelectric ceramics were prepared by the conventional ceramic technique. Sintering characteristic of Ca 0.82 (NaCe) 0.09 Bi 4 Ti 4 O 15 was discussed. The X-ray powder diffraction pattern showed a single phase of bismuth oxide layer structure having general formula (Bi 2 O 2 ) 2+ (A m −1 B m O 3 m +1 ) 2− with m =4. Scanning electron microscope (SEM) micrographs of the natural surface of ceramic samples indicated that the anisotropy of growth of grains becomes stronger with the increase in the sintering temperature. With the increase in the sintering temperature, the resistivity and piezoelectric constant d 33 increased to a maximum value and then decreased, but the dielectric constant e 33 T / e 0 decreased. The Curie temperature and the capacitance temperature stability of the ceramics were improved with the increase in the density.

Electrical properties of nitrogen incorporated tetrahedral amorphous carbon films

Abstract The electrical properties of nitrogen incorporated tetrahedral amorphous carbon (ta-C:N) films studied by Hall measurements over the range of 15–300 K were reported. Results indicated that the electrical properties of ta-C:N films are related to nitrogen pressure, which was the only variable during film deposition. The electrical resistivity of the ta-C:N films decreases with nitrogen pressure, accompanied by an increase of nitrogen concentration in the films. The influence of thermal annealing on the electrical properties of ta-C:N films was also investigated. The variation of the electrical properties of ta-C:N films may arise from the development of graphite-like structures in these films due to the incorporated nitrogen and annealing effects.

Formation of columbite-type precursors in the mixture of MgO-Fe2O3-Nb2O5 and the effects on fabrication of perovskites

Abstract All possible combinations of the three oxides, MgO, Fe 2 O 3 and Nb 2 O 5 have been investigated to trace the phase development during calcination by means of X-ray diffraction (XRD). It has been found that for the ternary system MgO–Fe 2 O 3 –Nb 2 O 5 , the phase evolvement in the process of calcining is not the simple superimposition of the three binary systems MgO–Fe 2 O 3 , MgO–Nb 2 O 5 and Fe 2 O 3 –Nb 2 O 5 . The reaction existing in the binary system MgO–Fe 2 O 3 no longer appears in the ternary system. Furthermore, Mg 4 Nb 2 O 9 , as a by-product of the binary system MgO–Nb 2 O 5 , does not form in the ternary system. Different precursors have different influence on the fabrication of perovskites. The possible mechanisms are discussed in detail.

Dielectric properties and dielectric aging of 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3 doped with CaO

Abstract The relaxor ferroelectric, 0.9Pb(Mg 1/3 ,Nb 2/3 )O 3 –0.1PbTiO 3 (0.9PMN–0.1PT) doped with different concentrations of CaO, was studied. Doping with CaO can increase the grain size of 0.9PMN–0.1PT ceramics. The dielectric properties and dielectric aging of this ceramic were studied. The maximum value of dielectric constant decreased and the degree of diffuse phase transition (DPT) enhanced with CaO doping. Also, obvious aging effects were found in the 0.9PMN–0.1PT doped with CaO. Through the analysis, it can be expected that Ca 2+ ions enter the lattice partly substituting for the Nb 5+ or Ti 4+ ions at B-sites.

Surface morphology of nitrogen doped tetrahedral amorphous carbon films on silicon by atomic microscopy imaging

Abstract The results of studies of the surface morphology of nitrogen doped tetrahedral amorphous carbon (ta-C) films with atomic force microscopy (AFM) are reported. The films were prepared by filtered arc deposition (FAD). N is introduced into the films during growth by injecting N 2 gas into a plasma stream formed by a carbon cathode vacuum arc. AFM revealed that the surface on formed films is uniform and smooth on the nanometerscale and the root-mean-square roughness of the films surface is calculated to be approximately 0.23–0.26 nm. The influence of N doping on the surface morphologies of ta-C films are discussed.

Effects of Processing Routes on Structures and Dielectric Properties of Lead Iron Niobate-Lead Magnesium Niobate Binary System

The binary system of lead magnesium niobate [Pb(Mg1/3Nb2/3)O3, PMN] and lead iron niobate [Pb(Fe1/2Nb1/2)O3, PFN] has been chosen to investigate the influence of different preparation routes on the microstructures and properties by means of X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersion spectrometer (EDS) and dielectric measurements. It is found that for the binary system (1-x)PFN–xPMN, the change in Curie temperature is approximately linear with respect to PMN content in the range of x=0 to 0.5. With the increase in x, the Curie points shift to lower temperatures. Both calcining and sintering conditions have a non-negligible influence on the microstructure and the dielectric properties. The dielectric and other properties of samples prepared by single-step and two-step precalcination routes are compared and the possible mechanisms are discussed. Samples mixed-sintered at an appropriate temperature exhibit a different dielectric behavior, which is also discussed in detail in this paper.

Compositional and morphological study of reactive ion beam deposited AlN thin films

Abstract AlN thin films were prepared on Si(1 0 0) substrates by reactive ion beam coating (RIBC). The composition and morphology of these films have been analyzed through non-Rutherford backscattering (NBS), Auger electron spectroscopy (AES) and atomic force microscopy (AFM). It was found that the A1/N ratio and the surface morphology depend on the deposition conditions. We also concluded that those films which are nearly stoichiometric all have smooth surfaces. When beyond stoichiometry, the surplus A1 atoms will condense to form protruding tips.

Effects of Different Dopants on Diffuse Phase Transition and Ordering Degree in Lead Magnesium Niobate

This work is based on the relaxor ferroelectrics lead magnesium niobate (PMN) system. The influences of different dopants (Li+, Sr2+, Y3+) on diffuse phase transition and ordering degree were studied. X-ray diffraction (XRD), high-resolution electron microscopy (HREM), selected area electron diffraction (SAED) and Raman spectroscopy were used to study small changes of ordering degree in PMN systems. Results showed that diffuse phase transition (DPT) is caused by the formation of an ordered structure at B-sites (Mg2+:Nb5+=1:1). The degree of DPT can be contrasted from dielectric properties, and has a direct relation with ordering degree of the microstructure. It also showed that, when doping with an element of one valence (Li+), the ordering degree of PMN was decreased; when doping with Sr2+ and Y3+, the ordering degree was enhanced to different extents.

OPTICAL PROPERTIES IN INFRA-RED REGION OF NITROGEN-INCORPORATED AMORPHOUS CARBON FILMS

Abstract Nitrogen-incorporated amorphous carbon (a-C:N) films are prepared by filtered arc deposition. Optical properties of a-C:N films were characterized by infra-red reflectance spectrometer. The experimental results show that the reflectivity of a-C:N films increases as the nitrogen content increases. Using detailed theoretical analysis and computer simulation, the complex dielectric constant ϵ = ϵ1 + iϵ2,, refractive index n = n + ik and absorption coefficient α of a-C:N films in infra-red region were investigated. Simulation results indicate that the optical constants of a-C:N show a considerable variation with wave number and nitrogen content. The a-C:N film with a low nitrogen content possesses a low ϵ and corresponding low n α values. The variation of optical properties and optical constants of a-C:N films may be due to the development of graphite-like structure with the increasing of nitrogen content in these films.