C Axis Preferred The Of Na <sub> X </ Sub> Coo <sub> 2 </ Sub> The Polycrystalline Preparation And Laser Induced Transverse Voltage Research

NaxCoO2has a hexagonal layered structure consisting of stacks of two-dimensional conductive CoO2planes and insulating Na+ions layer along the c-axis. It is a typical electron crystal-phonon glass material with large thermopower, low resisitivity and thermal conductivity. NaxCoO2has large structure and thermoelectric anisotropy, and it is a typical material of atomic layer thermopile.The highly c-axis oriented polycrystalline NaxCoO2(x=0.3-0.9), NaxCo1-yCuyO2(y=0.05,0.1,0.15) and NaxCo1-yMnyO2(y=0.05) bulks were prepared by solid-state reaction process. The phase and grains structure have been observed by XRD and SEM, the resistivity variation via Na contents and Cu, Mn doping effect have been analysed by R-T curve measurement. The laser induced transverse voltage (LITV) effect in polycrystalline NaxCoO2ceramic has been observed firstly; grains size and structure anisotropy are the major effecting factors for the LITV peak value. The c-axis oriented Na0.6CoO2films have been deposition on Al2O3substrates by pulse laser deposition (PLD) techniques, and the temperature dependent of resistivity showes metallic behavior.Through contrast different sinter processes and analysing DT/TGA, sinter process760℃/12h+830℃/24h+870℃/40h has been adopted. NaAlO2powder had been produced by the reaction of evapor Na and Al2O3crucible at contact surface, and pasted on sample phase.In the range0.3-0.9, the suitable sinter temperature increases with increasing Na contents;870℃is beneficial to high Na contents (x=0.6-0.8) bulk sintering. The SEM observations show that the crystal grains are stacked not very order; in Nao.5Co02polycrystal, there are many small grains adsorp on lager grains, and that decreased with increaseing Na content, dispeared in x=0.7,0.8. In the range of0.5-0.9, the c-axis lattice parameter of NaxCoO2decrease by increasing Na contents, the resistivity with increasing Na contents present down in the range of0.5-0.6and raise in0.6-0.9.Mn doping has decreased grain size. The temperature dependent of resistivity of Na0.5Co0.95Mn0.05O2is2-3orders of magnitude lager than that of undoping sample, and shows insulate behavior. Under further920℃/10h sintering, the resistivity of Na0.5Co0.95Mn0.05O2sample changes into metallic behavior. Cu doping has increased grain size and decreased c-axis texture, the resistivity of Na0.7Co1-xCuxO2is lower than that of undoping sample.The artificial inclined surface has been construct in Na0.67CoO2bulk, and then connect to the LITV measurement. Under irradiation of pulsed laser, the LITV signals were observed on inclined surface with peak voltage200mV-500mV, rise time30ns-43ns;the LITV peak values show a linear dependence of laser energy densities. Na0.71CoO2bulk which sintered by760℃/12h+830℃/24h has smaller grains size, smaller anisotropy of grains structure, higher resisitivity than the further870℃/40h sinter Na0.67CoO2bulk, and that induced smaller peak value, longer rise time in Na0.71CoO2bulk.