A glass-ceramic processing is applied to a glass with the composition of 33.3Li 2 O-33.3V 2 O 5 -33.3P 2 O 5 (mol%) in order to synthesize lithium ion-conductive b-LiVOPO 4 crystals being a potential candidate for cathode materials in lithium ion batteries. It is found that three crystalline phases of a-LiVOPO 4 , Li 2 VPO 6 , and b-LiVOPO 4 are formed during the crystallization and a-LiVOPO 4 crystals formed initially transform into b-LiVOPO 4 . The glass-ceramics consisting of almost mainly b-LiVOPO 4 crystals are successfully prepared by a heat treatment at around 6001C in air. The glass-ceramics with b-LiVOPO 4 crystals show the electrical conductivity of 1.7 Â 10 À7 S/cm at room temperature and the activation energy of 0.38 eV in the temperature range of 251-2401C. The structure and electrical properties of the precursor glass are also examined. The present study proposes that the glass-ceramic processing has an advantage for the fabrication of b-LiVOPO 4 crystals, because it is difficult to synthesize b-LiVOPO 4 crystals using a conventional powder-sintering method.
The formation mechanism of LiFePO 4 crystals in lithium iron phosphate glass (33.3Li 2 O33.3Fe 2 O 3 33.3P 2 O 5 ) particles with a diameter of <63¯m was investigated by using X-ray diffraction (XRD) and high resolution transmission electron microscope (HRTEM) techniques. LiFePO 4 was mainly crystallized by heat treatments at 350800°C for 30 min under 7%H 2 /Ar atmosphere. At low temperature heat treatments, nano-scaled (³40 nm) Li x FePO 4 crystallites are formed through a homogeneous nucleation process. With increasing temperature, a contribution of the reduction of Fe 3+ to Fe 2+ becomes larger, and LiFePO 4 grows from the surface toward the inside of particles. Li 3 Fe 2 (PO 4 ) 3 and Fe 2 O 3 crystals with Fe 3+ are formed in the inside. In the heat treatment at 800°C, the formation of LiFePO 4 crystals is largely promoted through the reduction of Fe 3+ and the phase transition of Li 3 Fe 2 (PO 4 ) 3 and Fe 2 O 3 crystals. An existence of amorphous layer with a thickness of several nm between the crystallites is confirmed even in the well crystallized sample from HRTEM observations.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.