W.C. Chen

Enhanced dielectric properties of Ba1-xSrxTiO3 thin film grown on La1-xSrxMnO3 bottom layer

The Ba{sub 0.7}Sr{sub 0.3}TiO{sub 3} (BST)/La{sub 0.67}Sr{sub 0.33}MnO{sub 3} (LSMO) heterostructure has been fabricated by pulsed-laser deposition on (001) SrTiO{sub 3} single crystal substrate. The crystallization and surface morphology of the heterostructure have been characterized by x-ray diffraction and atomic force microscopy. The composition distribution along the depth of the heterostructure is analyzed by Auger electron spectroscopy. It is founded that the LSMO bottom layer shows a marked effect on the dielectric properties of the BST films. Comparing with BST/YBCO (YBCO-YBa{sub 2}Cu{sub 3}O{sub 7}) heterostructure grown by similar process, the dielectric loss exhibits much lower and less frequency dispersive, especially in the high frequency region. The loss tangent at 100 kHz is about 0.012 and the figure of merit factor is about 25 under the condition of 200 kV/cm. Ferroelectric hysteresis measurement shows that the remanent polarization and coercive field of the heterostructure are 3.4 {mu}C/cm{sup 2} and 39 kV/cm, respectively. These parameters are all better than BST/YBCO heterostructure. The good surface morphology and the element diffusion between BST and LSMO layers may be suggested to be responsible for the above-improved parameters of BST/LSMO heterostructure.The Ba0.7Sr0.3TiO3(BST)∕La0.67Sr0.33MnO3(LSMO) heterostructure has been fabricated by pulsed-laser deposition on (001) SrTiO3 single crystal substrate. The crystallization and surface morphology of the heterostructure have been characterized by x-ray diffraction and atomic force microscopy. The composition distribution along the depth of the heterostructure is analyzed by Auger electron spectroscopy. It is founded that the LSMO bottom layer shows a marked effect on the dielectric properties of the BST films. Comparing with BST∕YBCO (YBCO—YBa2Cu3O7) heterostructure grown by similar process, the dielectric loss exhibits much lower and less frequency dispersive, especially in the high frequency region. The loss tangent at 100kHz is about 0.012 and the figure of merit factor is about 25 under the condition of 200kV∕cm. Ferroelectric hysteresis measurement shows that the remanent polarization and coercive field of the heterostructure are 3.4μC∕cm2 and 39kV∕cm, respectively. These parameters are all better than...

The influence of pH on the habit and the rate of α-LiIO3 crystal growth

Abstract The influence of the pH on both the habit and the growth rate of α-LiIO 3 crystals grown from solution by a constant temperature evaporation method has been studied under static and rotary conditions. The results indicated that the morphology of the α-LiIO 3 crystals grown had hexagonal prismatic faces {10ovbar|10} and hexagonal double pyramidal faces {10ovbar|11} and that the crystal growth rates along the z -direction V [0001] were faster than the rates in the opposite z -direction V [000 1 ] if the pH was more than a critical amount (pH c ). If however, the pH was less than pH c , then the crystal habit was bounded by the prismatic faces {10ovbar|10} and the pyramidal faces {10ovbar|11} and {12ovbar|32}, and V [0001] was slower than V [000 1 ] . The mechanism to explain the reversal of the growth rate at pH c was proposed by means of the electrical double layer theory and the molecular adsorption theory.

The determination of solute distribution during growth and dissolution of NaClO3 crystals: the growth of large crystals

The solute concentration distribution close to solid/liquid interfaces has been determined by Mach-Zehnder interferometric technology during crystal growth and dissolution processes of NaClO3. A fringe carrier technique was introduced to visualize more clearly the boundary layer and to solve the concentration distribution. Solubility of NaClO3 in aqueous solution from 29.2 to 47.4degreesC was also measured by both an optical interferometer and weight techniques. The experimental results indicate that the boundary layer thickness in the NaClO3 solution depends on the fluid dynamical conditions, the crystal faces and the local position. Large crystals of NaClO3 were grown using seeds, which were nucleated and developed at 50degreesC. Transparent crystals having sizes of more than 34 mm, x 36 mm. x 40 mm were successfully grown by a cooling temperature method. NaClO3 crystals have been chosen as a representative candidate for space experiments in our laboratory

Growth of α-LiIO3 crystal under microgravity conditions

The growth of the α-LiIO 3 crystals in space was carried out in a Chinese return satellite. 14 boules of α-LiIO 3 single crystals were grown during 8 days in space. The morphology, growth rate and quality of the crystals were assessed by microscopic and X-ray topographic techniques. The experimental results show that the quality of space grown crystals is better than the earth grown crystals. The crystal growth rate along the [10001] c -axis in space is faster than that on earth. The crystal habits does not change.

Post-research on α-LiIO3 crystal growth in space

The experimental results on crystal growth of alpha-LiIO3 in space indicated that the critical pH value of alpha-LiIO3 solution, pH,, is increased under microgravity environment as compared with the experimental findings on the earth. For investigating a mechanism of space crystal growth of alpha-LiIO3 and explaining space experimental phenomena, a solid/liquid boundary layer characteristic and solute concentration distribution has been determined by the Mach-Zehnder interferometric technology during crystal growth and dissolution processes of alpha-LiIO3. A fringe carrier technique is introduced to visualize more clearly the boundary layer and solve the concentration distribution. The crystal growth rate of alpha-LiIO3 was measured and calculated. The experimental findings show that the growth rate and the boundary layer characteristics are influenced by natural convection. The concentration distribution along [0 0 0 1] and [0 0 0 (1) over bar] directions are markedly different. The growth rates on the (1 0 (1) over bar(1) over bar) faces are similar to that on (1 0 (1) over bar (1) over bar) faces at pH of 4.06. This finding could be beneficial for understanding the experimental space results on crystal growth. alpha-LiIO3

Study of α-LiIO3 single crystals grown in space

alpha-LiIO3 single crystals were grown by the aqueous solution method with a pH value from 3.6 to 12 in Chinese Scientific recoverable satellites. The morphology of the crystals grown in space is similar to that of earth-grown crystals. The growth rate of the crystals is influenced by both the pH value of solution and gravity except for the solution concentration. It is found that the growth rates of the positive and negative sides of the space-grown crystals are almost the same in a solution with pH=4.02. The perfection of both crystals grown in space and on the earth was examined by X-ray topography.

Influence of Mg2+ ions doping on the structure, morphology and phase transition of LiIo(3) crystal

The influence of different concentrations of Mg2+ ions doping on the structure, morphology and phase transition of LiIO3 crystal was investigated. The best Mg2+-doped alpha-lithium iodate (Mg:alpha-LiIO3) crystals for potential optical applications can be successfully grown by the aqueous solution method when the concentration of Mg2+ ions in the initial mother solutions C-m 1. The polarized Raman results are consistent with our conclusions that the Mg2+ ion substitutes for the host Li+ cation in the pure alpha-LiIO3 crystals and results in the corresponding cation vacancies. As C_ increases, inclusions, spontaneously crystalline grains, 3 phase of LiIO3 and hillock-shape Mg:alpha-LiIO3 crystals are induced respectively by different concentrations of Mg2+ ions doping under the same crystal growth conditions. When C-m > 0.1 M, the polarized Raman results indicate that larger amounts of Mg2+ ions incorporated inhibit LiIO3 growth and result in the hillock-shape morphology by destabilizing the crystal lattice and inducing lattice distortion.