Chemical potential induced phase transition in the metallic electrode attached to the ferroelectric Pb5Ge3O11 single crystal

The metallic contact electrode was attached to the one surface of the ferroelectric semiconducting Pb5Ge3O11 single crystal and at opposite ends of this electrode wires were glued. A voltage has been applied to the wires and the resistance R of the contact electrode has been measured as function of temperature on heating and cooling. Two series of independent measurements were carried out where the ferroelectric c-axis of the Pb5Ge3O11 uniaxial crystal was perpendicular and parallel to the contact electrode. They revealed change in slope (a kink) of the contact electrode resistance curve at the critical point Tkink≈452K. This result was obtained for both gold and silver electrode materials. The critical temperature Tkink exactly corresponds to the Curie temperature TC of the transition between the ferroelectric (P3) and paraelectric (P6¯) phases of the Pb5Ge3O11 single crystal. This effect is the evidence that the chemical potential induced secondary phase transition takes place in the electron gas of the contact electrode and it results in the irregularity of the resistance temperature dependence at the critical point. The contact electrode method can be succesfully used to detect the critical temperature without necessity to apply external electric field to the crystal sample. The method works well also in the case of non-metallic materials like Pb5Ge3O11 and not only for metallic samples reported in the literature before.