Shuxia Shang

Bi3.25La0.75Ti3O12 thin films prepared on Si (100) by metalorganic decomposition method

Bi3.25La0.75Ti3O12 (BLT) thin films have been grown on n-type Si (100) substrates by metalorganic decomposition method. The structural properties of the films were examined by x-ray diffraction. The BLT films exhibit good insulating property with room temperature resistivities in the range of 1012–1013 Ω cm. The current–voltage characteristics show ohmic conductivity in the lower voltage range and space-charge-limited conductivity in the higher voltage range. The capacitance–voltage characteristic hysteresis curves show that the metal-ferroelectric-semiconductor structure has memory effect. The fixed charge density and the surface state density were also calculated. The results obtained indicate that the present BLT films are suitable for making ferroelectric field effect transistor memories.

Preparation and properties of Bi4Ti3O12 single‐crystal thin films by atmospheric pressure metalorganic chemical vapor deposition

Bismuth titanate (Bi4Ti3O12) thin films have been grown on (100) silicon substrates at 550 °C by atmospheric pressure metalorganic chemical vapor deposition using Bi (C6H5)3 and Ti (OC4H9)4 as the source materials. The x‐ray diffraction analysis and reflection electron diffraction pattern revealed that the film is a single crystal with a (100) orientation. Ferroelectric properties were confirmed by polarization hysteresis curve observation. The remanent polarization and coercive field were found to be 38 μC/cm2 and 45 kV/cm, respectively. The measured dielectric constant and loss tangent were 93 and 0.05, respectively, at room temperature.

Effect of thermal annealing on structural properties, morphologies and electrical properties of TiO2 thin films grown by MOCVD

TiO2 thin films, were deposited on Si(100) and Si(111) substrates by metalorganic chemical vapor deposition at 500 °C, and have been annealed for 2 min, 30 min and 10 hours at the temperature from 600 °C to 900 °C, in oxygen and air flow, respectively. XRD and atomic force microscopy characterized the structural properties and surface morphologies of the films. As-deposited films show anatase polycrystalline structure with a surface morphology of regular rectangled grains with distinct boundaries. Rutile phase formed for films annealed above 600 °C, and pure rutile polycrystalline films with (110) orientation can be obtained after annealing under adequate conditions. Rutile annealed films exhibit a surface morphology of equiaxed grains without distinct boundaries. The effects of substrate orientation, annealing time and atmosphere on the structure and surface morphology of films have also been studied. Capacitance-Voltage measurements have been performed for films deposited on Si(100) before and after annealing. The dielectric properties of TiO2 films were greatly improved by thermal annealing above 600 °C in oxygen.

Possible presence of 2234 phase with Tc(zero) of 95 K in a Bi‐Pb‐Sb‐Sr‐Ca‐Cu‐O ceramic

Samples of Bi1.84Pb0.34Sb0.1Sr2Ca2Cu3Oy ceramic were prepared by a direct sintering and air quenching method. A new phase with Tc(zero) of 95 K is detected inside multiphased samples by resistivity and susceptibility measurements. Powder x‐ray diffraction analysis indicates that the structure is orthorhombic with cell parameters a=5.41 A, b=5.44 A, c=43.35 A. The (Bi, Pb)2Sr2Ca3Cu4Oy composition is determined by x‐ray energy dispersion analysis.

Ferroelectric Thin Films of Bismuth Titanate Prepared by Mocvd

The ferroelectric thin films of bismuth titanate (Bi 4 Ti 3 O 12 ) have been prepared by metalorganic chemical vapor deposition ( MOCVD) technique at atmosphere. The triphenyl bismuth (Bi(C a H 5 ) 3 )and tetrabutyl titanate (C 16 H 36 O 4 Ti) were used as precursors. Dense Bi 4 Ti 3 O 12 films with smooth shinning surface have been grown on Si( 100) substrates at 550°C whithout postannealing. The as- grown films were characterized by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and energy dispersion analysis ( EDAX). The films showed well-ordered crystallinity with an (001)preffered orientation. The influence of growth parameters on deposition rate, composition and morphology of as-grown films was also discussed.

STUDY OF THE GROWTH PROCESS OF LARGE SIZE BSCCO CRYSTALS

The growth process of large size BSCCO crystal has been studied. BSCCO crystals with the size of 15 X 4 X 2 mm 3 have been grown by self-flux method. The a-b plan is spotless and smooth. The results obtained from the measurements of resistivity and a.c. susceptibility show that Tc(zero) is 90K. During the crystal growth process, high temperature gradient and three-step process were used. The single crystals obtained have better cleavage. Differential thermal analysis of BSCCO crystal was also made.

EFFECT OF Sb OR Cd ADDITION ON THE FORMATION OF SUPERCONDUCTING PHASES IN THE Bi-BASED SYSTEM

The effect of Sb or Cd addition on the formation of superconducting phases in the ceramic samples of Bi 1.84 Pb 0.34 Sb 0.1 Sr 2 Ca 2 Cu 3 O y and Bi 1.84 Pb 0.34 Sr 2 Ca 2 Cd x Cu 3 O y (x=0.1 to 1 in step of 0.1) has been studied by using a direct sintering and air quenching technique. The measurements of resistivity and a.c. susceptibility show that there are two main phases in the Sb-doped sample, one is 2223 phase, the other is 2234 phase with Tc(zero) and cell parameter c of 95K and 43.35a, respectively. For Cd-doped samples, Tc(zero) decreased slightly with the increased doping of Cd, and the X-ray diffraction patterns reveal that 2212 phase is the main phase in these samples.

GROWTH OF LaAlO 3 SINGLE CRYSTAL BY VERNEUIL METHOD

Single crystal of LaAlO 3 have been grown by Verneuil method. The powders of Al 2 O 3 (99.90%) and La 2 O 3 (99.99%) were used as starting materials. The crystals with size up to Φ15 X 25 m 3 and light brown colour were obtained. The XRD analyses show that the LaAlO 3 crystal have hexagonal structure with lattice parameter of a=b=5.365a and c=13.114a. The dielectric constant and dissipation were measured by using HP 4192A LF Impedance Analyzer at temperature from 77K to 300K and frequency from 1 KHz to 13 MHz. At room temperature the dielectric constant is 24.3 and the dissipation is less than 1 X 10 -3 .

THE INFLUENCE OF Sr/Ca RATIO ON THE SUPERCONDUCTIVITY OF Bi-Sr-Ca-Cu-O CRYSTALS

Crystals grown from Bi-Sr-Ca-Cu-O system may have different contents of Sr and Ca when varying the ratio of Sr/Ca in the starting composition. The Sr/Ca ratio in crystal has important influence on the superconducting property of Bi-Sr-Ca-Cu-O crystal. The lattice parameter c increased from 30.60A to 31.01A and Tc(zero) increased from 84K to 90K with the increasing of Sr/Ca ratio from 2:1 to 3:1 accordingly. This result has shown its importance for understanding high-Tc superconducting phenomenon in Bi-Sr-Ca-Cu-O system further.