Dielectric properties of “weak” ferroelectric Li₂Ge₇O₁₅

Abstract

The detailed studies of the anomaly of electric permittivity ε for Li₂Ge₇O₁₅ (lithium heptogermanate) in the region of phase transition have been described in this paper. The measurements of ε(T) in heating and cooling processes have been carried out. The well seen maximum of the electric permittivity (which value is different for heating and cooling processes) has been observed. The Curie-Weiss law is fulfilled only in the narrow temperature range near T_c .; the Curie constant is equal to 2.6 K in the para-phase and 1.3 K—in the ferrophase. The measurements of ε(T) in the presence of a constant electric field have shown that the value of ε_max decreases with the increase of the external electric field. It has been revealed that the value of the maximum electric permittivity decreases in the cooling process and it remains constant in the heating process. This fact confirms the hypothesis about the existence of the internal electric field in the sample during the heating process.

Key Words:

• ‘Weak’ ferroelectric
• phase transition
• dielectric properties
• Li₂Ge₇O₁₅