Formation of LiV₂O₅ Needle Crystals by the Reduction of the Molten Li₂O-V₂O₅ System

Abstract

When the molten Li₂O-V₂O₅ system was reduced in the atmosphere of the H₂-Ar mixed gas at 750-800°C for 5-20 hrs, LiV₂O₅ needle crystals, frequentry reaching 10 mm long and above, were formed in the melt. The needle crystals were grown from the melt of three kinds of compositions i. e. Li₂O: V₂O₅=1: 2, 2: 3 and 1: 1 in mole ratio. The experimental condition to get larger needle crystal was proved as follows; Li₂O: V₂O₅=1: 1, flow rate of reducing gas; H₂(8 ml/min)-Ar(300 ml/mm), temperature; 750°C, duration; 5 hr. Needle crystal reaching O.2 x 1 x 25 mm in size were grown under above conditions.
Equilibrium oxygen partial pressure for the formation of LiV₂O₅ from the melt of 1: 1composition was measured by means of oxygen concentration cell composed stabilized ZrO₂ and the relation between the oxygen partial pressure and absolute temperature at 973-1123°K was revealed as follows; log Po₂= -11800/T+4.79 The temperature dependence of free energy for the formation of LiV₂O₅ was represented as a following equation, ΔG⁰=-54000+21.9 T (cal/mol)
By the back Laue diffraction technique, it was found that the growth direction of needle crystal was <010> and the largest face of the crystal occurred was (001).
The crystal showed a semiconductive property. Its electrical resis tivity along to <010> was 5 to 20 Ω ⋅cm at room temperature and its activation energy was about 0.30 eV at the tempera ture from -20 to 150°C.