Heavy metal selenides have shown very good properties including wavelength conversion in MWIR and LWIR regions, acousto-optic and great potential for radiation detection. We have extensively studied thallium-based compounds for variety of applications. Studies were performed for crystal growth, fabricability and radiation detection characteristics of ternary congruent compounds of thallium mercury iodide system from the melt by Bridgman method. The congruency and phase transition was studied by DTA. Material melts congruently between 300-400 0C and do not show any other phases between room temperature and melting point. Crystal slabs were fabricated as bulk detector to demonstrate good characteristics for detectivity of X-ray and gamma-rays. Effect of impurities on performance were evaluated by using source materials of different purity for synthesis. Crystals with high purity source materials and mixed by vibrating method were determined for resistivity in range of 1012ohm-cm.
Polarity is very important in developing materials with colossal dielectric. To meet the demands for the tunable devices and high dielectric parallel plate capacitors, several perovskites such as CaCu3Ti4O12 (CCTO), La2/3Cu3Ti4O12 (LCTO) Pr2/3Cu3Ti4 O12 (PCTO) and several other materials of this class have been studied all over the world. Detailed studies showed that results vary a lot based on processing methods, such as powder vs. multi crystals and single crystals. In spite of great progress in processing, low resistivity and process driven variables in properties remain a big hurdle for its applications as a dielectric capacitor. We observed that dielectric values are significantly changed when these materials are exposed to chemicals and biological agents. We used parallel plate capacitor design for making chemical and biological sensors from CCTO member of this group. The data indicated huge difference in the dielectric and resistivity of the exposed samples.
Zinc doped titanium oxide (Ti1-xZnxO2, x=0.05) abbreviated as Ti0.95 Zn0.05O2 (TZO) ceramic was synthesized by semiwet route using aqueous solution of zinc acetate dihydrate and solid titanium dioxide as starting materials. The single phase formation of the TZO ceramic sintered at 900 °C for 8 h was confirmed by powder X-ray diffraction (XRD) analysis. The lattice parameters obtained by Retvield refinement were found to be a=b= 4.609 Å, c= 2.967Å and α=β= γ= 90 ° with space group P 42/m n m confirmed the rhombic structure of TZO ceramic. The average particle size of the TZO ceramic observed by TEM analysis was found to be 84 nm. The surface morphologies and roughness parameters of TZO ceramic were observed by atomic force microscopy (AFM) analysis. The value of dielectric constant (ε′) and tangent loss (tan δ) of the TZO ceramic were found to be 230 and 0.2, respectively at 100 Hz and 498 K.
There are several mechanisms which have been proposed for the existence of colossal dielectric constant in the class of perovskite calcium copper titanate (CaCu3Ti4O12 or CCTO) materials. Researches indicate that existence of twinning parallel to (100) (001) and (010) planes causes planar defects and causes changes in local electronic structure. This change can cause insulating barriers locally which contribute to the large dielectric values irrespective of processing. The combination of insulating barriers, defects and displacements caused by twinning have been attributed to the generation of large dielectric constant in CCTO. To examine some of these arguments some researchers replaced Ca with other elements and evaluated this concept. In this study we present the synthesis and characterization of Ga2/3Cu3Ti4O12-xNx (GCTON) material. This provides both distortion due to atomic size difference and defects due to insertion of nitrogen. The morphology of the compound was determined to show that processing has tremendous effect on the dielectric values. The resistivity of GCTON was several order higher than CCTO and dielectric constant was higher than 10,000.
Dielectric properties of high percentage Mg doped CaCu3Ti4O12, CaCu3-xMgxTi4O12 (x=0.20 and 0.50) ceramics carried out. They were synthesized by the semi-wet route using a solution based citrate–nitrate method along with inexpensive solid TiO2 powder. X-ray diffraction analysis reveals that the ceramics form single phase when sintered at 950 °C for 12h. SEM analyses show the smooth surfaces of grains with a spherical appearance. The grains of CCMTO2 and CCMTO5 ceramics were found to be in the size range of 1-5 μm and 1-3 μm, respectively. Dielectric studies show that the CCMTO2 ceramic has higher value of dielectric constant and lower dielectric loss in comparison to that of CCMTO5.
Recent studies on multinary oxides for applications as laser hosts and high dielectric capacitors have shown that processing at high temperature provides glassy or crystalline materials based on thermal treatments and cooling rates. Since hydroxyapatites are now subject of great interests due to their bioactivity, interest in producing soft and hard materials with glassy and crystalline nature by processing parameters has become very important. Crystalline materials by using Bridgman, Czochralski and flux growth methods are costly and require huge investment. We have observed that even low temperature solidification in organic flux produced oriented fibers. This organic treated material has different characteristics than in situ oxide materials prepared by sintering and grain growth. Examples of phosphate and silicate-based systems will be presented to demonstrate soft and hard materials. Effect of TiO2 and other hardening elements will be also reported.
This study provides excellent method to create large surface area and morphologies which can be used in drug delivery and for absorption of drugs. In addition provides knowledge about morphological transition
We have prepared silicate based hard materials and have processed it with organic flux. Because of the bioactivities of hydroxyapatites with tissues, this class of materials have attracted interest for bone applications. We have utilized low temperature processing techniques. Organic melt was used and the directional solidification method to cast the shaped sample. This organic treated material has different characteristics than coarsened oxide materials. Our approach involved low temperature processing using nano and micron sized powders of the material system Na2OK2O- CaO- MgO-Ga2O3-SiO2, and titanates were processed by sintering and grain growth. Our results indicate that substitution of gallium and magnesium or titanium with some variation in processing methods have great potential to improve the glassy characteristics without decreasing the mechanical properties of bones. Effect of radiation on bone was studied by exposing with commercially available Cs137 gamma ray source. It was observed that electrical resistivity increased due to radiation exposure for this system.
Recently there is a big thrust on bio-inspired sensors and there has been a large rise in the investment and expectations for nanotechnology to meet these goals. For in situ sensor development materials deposition on substrate is essential part of device development. Physical vapor deposition (PVD), chemical vapor deposition (CVD) and molecular organic vapor deposition methods have developed for growth of semiconductor bulk and thin film growth with some modifications have been used for these materials. Oxides and other elements of VI group such as sulfides and selenides are key components in skins of many species. Growth of ordered structures containing these elements have been achieved by using PVD method. This paper describes effect of growth parameters during PVD growth on the quality of materials. Growth kinetics and mechanism will be discussed for the vertical and horizontal growth reactors. Since most of the efficient materials systems are multinary and in many cases noncongruent, PVD provides pathway to grow materials below melting temperature.
Since the report of high dielectric value was published for the calcium copper titanate of the stoichiometry CaCu3Ti4O12 (CCTO), several of its analogs such as Yittrium copper titanate Y2/3Cu3Ti4O12 (YCTO), Pr2/3Cu3Ti4O12 (PCTO) and several other compounds have been studied extensively. Most of these materials have demonstrated very high dielectric constants. However, the roadblock is their low resistivity. To overcome this problem, several approaches have been considered, including doping and substitution. In order to solve this problem, we have synthesized the stoichiometric composition and used low temperature processing to grow grains of La2/3Cu3Ti4O12 (LCTO) stoichiometric compound. LCTO with excess copper oxide was also prepared to determine its effect on the morphology and dielectric constant of the stoichiometric LCTO compound. In spite of the low melting point of copper oxide, we observed that excess copper oxide did not show any faster grain growth. Also, the dielectric constant of LCTO was lower than CCTO and unlike CCTO, LCTO showed significant changes as the function of frequency. The measured resistivity was slightly higher than CCTO.
The complex perovskite ACu3Ti4O12 (A = Ca, Bi2/3, Y2/3) which possess high dielectric constant could be promising candidates to replace relaxors as dielectrics in DRAM, MLCCs and other memory devices. Their smaller capacitive components lead to miniaturization of electronic devices with efficient performance. Yttrium Copper Titanate (Y2/3Cu3Ti4O12) nano-ceramic is structurally analogous to CaCu3Ti4O12. XRD of Y2/3Cu3Ti4O12 shows the presence of all normal peaks of CaCu3Ti4O12. SEM micrograph exhibits the presence of bimodal grains of size ranging from 1-2 μm. Bright field TEM image clearly displays nano-crystalline particle which is supported by presence of a few clear rings in the corresponding selected area electron diffraction pattern. It exhibits high dielectric constant (ε′= 8434) at room temperature and 100 Hz frequency with characteristic relaxation peaks.
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