The present work concerns sustainable development of environmentally compatible electronic materials. Our investigations have mainly focused on nonlinear orthophosphate compounds and more particularly on eulytite phas...The present work concerns sustainable development of environmentally compatible electronic materials. Our investigations have mainly focused on nonlinear orthophosphate compounds and more particularly on eulytite phases. Phosphate eulytites crystallize with the non centrosymmetric space group 1-43d which is compatible piezoelectronic and nonlinear optical properties. Indeed, second harmonic generation （SHG） tests performed on systems of the type BIIaMm（PO4）3 （with Bn= Cd, St, Ba, Pb; MIII= Ln, Bi） showed better performance than KDP （about 100 KH2PO4）1）＇2）. The practical interest of eulytite compounds has been evidenced by various authors in various domain of modem technology; i） medicine （positron tomography）, ii） nuclear industry （fuel rods control）, iii） high energy physics （CERN detector）, iv） etc. Indeed CERN in Geneva is currently using 1300 liters of Bi4（GeO4）3 single crystals. Then, bismuth silicates and bismuth germinate Bi4（SiO4）3 and Bi4（GeO4）3 have important applications in high energy physics as for example, scintillators （ionizing radiation detectors, etc.）. The main aim of our research work is to try to correlate between the chemical composition, the crystalline structure and the physical properties （optical, piezoelectric, etc.） of the phosphate eulytites free of toxic elements with various dopants （Ce3＋, Eu3＋, etc.）. As single crystals are of high cost and difficult to grow, glasses have low technological efficiency of our planed optical applications. Therefore, we are trying to prepare transparent ceramics which are expected to give rather excellent satisfaction. We prepared BaaBi（PO4）3 eulytite phases by two difference methods. One is based on the use of CO2 gas blowing in order to dissolve starting materials （like Baa（PO4）2） and crystallize pure eulytites. The second process is using the sol-gel method.展开更多
Various compositions of the system BaxSr1-xTiO3 (BST) have been elaborated both as fine powders and ceramic monoliths, using the co-precipitation route within a warmed supersaturated solution of oxalic acid. The appro...Various compositions of the system BaxSr1-xTiO3 (BST) have been elaborated both as fine powders and ceramic monoliths, using the co-precipitation route within a warmed supersaturated solution of oxalic acid. The appropriate stoichiometry was determined from the mixtures of precisely titrated aqueous solutions of cations chlorides (SrCl2, BaCl2, and TiCl4). The reason of this process was to apply low sintering temperature in production of BST samples with ultra-fine powders. These powders primarily calcined at (850°C) for (5 hr) were used to elaborate ceramics after pellets sintering at (1200°C) during (8 hrs). Indeed, XRD patterns were confirmed that the samples are a pure phase and a perovskite cubic structural type at (x = 0, 0.5, 0.6). Whereas, (x = 0.7, 0.8, 0.9, 1) showed a tetragonal phase. There is agreement between the FTIR and XRD analysis, by the relation of the wave vector (K) and lattice constant. It was deduced a stimulated relation between (x) and (K). The results of TEM, they were clear that the lowest particle sizes investigated of BST powders nearly (36 - 50 nm).展开更多
CaCu_(3)Ti_(4-x)Y_(x)O_(12)(0≤x≤0.12)ceramics were fabricated with conventional solid-state reaction method.Phase structure and microstructure of prepared ceramics were characterized by X-ray diffraction(XRD)and sca...CaCu_(3)Ti_(4-x)Y_(x)O_(12)(0≤x≤0.12)ceramics were fabricated with conventional solid-state reaction method.Phase structure and microstructure of prepared ceramics were characterized by X-ray diffraction(XRD)and scanning electron microscopy(SEM),respectively.The impedance and modulus tests both suggested the existence of two different relaxation behavior,which were attributed to bulk and grain boundary response.In addition,the conductivity and dielectric permittivity showed a step-like behavior under 405 K.Meanwhile,frequency independence of dc conduction became dominant when above 405 K.In CCTO ceramic,rare earth element Y^(3+)ions as an acceptor were used to substitute Ti sites,decreasing the concentration of oxygen vacancy around grainelectrode and grain boundary.The reason to the reduction of dielectric behavior in low frequencies range was associated with the Y doping in CCTO ceramic.展开更多
文摘The present work concerns sustainable development of environmentally compatible electronic materials. Our investigations have mainly focused on nonlinear orthophosphate compounds and more particularly on eulytite phases. Phosphate eulytites crystallize with the non centrosymmetric space group 1-43d which is compatible piezoelectronic and nonlinear optical properties. Indeed, second harmonic generation （SHG） tests performed on systems of the type BIIaMm（PO4）3 （with Bn= Cd, St, Ba, Pb; MIII= Ln, Bi） showed better performance than KDP （about 100 KH2PO4）1）＇2）. The practical interest of eulytite compounds has been evidenced by various authors in various domain of modem technology; i） medicine （positron tomography）, ii） nuclear industry （fuel rods control）, iii） high energy physics （CERN detector）, iv） etc. Indeed CERN in Geneva is currently using 1300 liters of Bi4（GeO4）3 single crystals. Then, bismuth silicates and bismuth germinate Bi4（SiO4）3 and Bi4（GeO4）3 have important applications in high energy physics as for example, scintillators （ionizing radiation detectors, etc.）. The main aim of our research work is to try to correlate between the chemical composition, the crystalline structure and the physical properties （optical, piezoelectric, etc.） of the phosphate eulytites free of toxic elements with various dopants （Ce3＋, Eu3＋, etc.）. As single crystals are of high cost and difficult to grow, glasses have low technological efficiency of our planed optical applications. Therefore, we are trying to prepare transparent ceramics which are expected to give rather excellent satisfaction. We prepared BaaBi（PO4）3 eulytite phases by two difference methods. One is based on the use of CO2 gas blowing in order to dissolve starting materials （like Baa（PO4）2） and crystallize pure eulytites. The second process is using the sol-gel method.
文摘Various compositions of the system BaxSr1-xTiO3 (BST) have been elaborated both as fine powders and ceramic monoliths, using the co-precipitation route within a warmed supersaturated solution of oxalic acid. The appropriate stoichiometry was determined from the mixtures of precisely titrated aqueous solutions of cations chlorides (SrCl2, BaCl2, and TiCl4). The reason of this process was to apply low sintering temperature in production of BST samples with ultra-fine powders. These powders primarily calcined at (850°C) for (5 hr) were used to elaborate ceramics after pellets sintering at (1200°C) during (8 hrs). Indeed, XRD patterns were confirmed that the samples are a pure phase and a perovskite cubic structural type at (x = 0, 0.5, 0.6). Whereas, (x = 0.7, 0.8, 0.9, 1) showed a tetragonal phase. There is agreement between the FTIR and XRD analysis, by the relation of the wave vector (K) and lattice constant. It was deduced a stimulated relation between (x) and (K). The results of TEM, they were clear that the lowest particle sizes investigated of BST powders nearly (36 - 50 nm).
基金This work was financially supported by the Natural Science Foundation of China(Grant Nos.11564010,11264010,21061004 and 50962004)by the Natural Science Foundation of Guangxi(Grant No.GA139008).
文摘CaCu_(3)Ti_(4-x)Y_(x)O_(12)(0≤x≤0.12)ceramics were fabricated with conventional solid-state reaction method.Phase structure and microstructure of prepared ceramics were characterized by X-ray diffraction(XRD)and scanning electron microscopy(SEM),respectively.The impedance and modulus tests both suggested the existence of two different relaxation behavior,which were attributed to bulk and grain boundary response.In addition,the conductivity and dielectric permittivity showed a step-like behavior under 405 K.Meanwhile,frequency independence of dc conduction became dominant when above 405 K.In CCTO ceramic,rare earth element Y^(3+)ions as an acceptor were used to substitute Ti sites,decreasing the concentration of oxygen vacancy around grainelectrode and grain boundary.The reason to the reduction of dielectric behavior in low frequencies range was associated with the Y doping in CCTO ceramic.
