Positron annihilation technique gives unique information for electronic structure of ferroelectric crystals. Anomalous change of property and structure parameters was compared with the theory of internal rotation of oxygen octahedra in lithium niobate single crystal. The experimental results can not be explained from the viewpoint of lattice dynamics. In temperature range of 20 to 85℃
the life-time spectrum of positron in LN has two major components. The ano-