Influence of space charges on ferroelectric property of weak ferroelectric Li2Ge7O15

Piezo-optic and Dielectric Behavior of the Ferroelectric Lithium Heptagermanate Crystals

“…The linear curve (Fig. 19) extrapolates to a T c = 281.5 K in the unstressed state instead of 283.5K as determined by dielectric measurements (Wada & Ishibashi, 1983;Kudzin et al, 1994Kudzin et al, , 1995. This may be due to a non linear dependence of shift of T c under stress near 283.5 K. Now we turn to the anomaly around T m .…”

“…17. The temperature dependence of the dielectric permittivity along the c-axis of LGO shows a sharp peak at T c (283.5 K) and the Curie-Weiss law holds only for a narrow range of temperature (T c ± 4 K) (Wada & Ishibashi, 1983;Kudzin et al, 1994Kudzin et al, , 1995 as shown in Fig. 6 and Fig.…”

“…Therefore it satisfies the law of two for the ratio of such derivatives of quantities which are coupled with the spontaneous polarization in second order ferroelectric phase transition such as in the case of triglycine sulphate (Haussuhl & Albers, 1977) and LGO. Therefore the peak around T c is (Kaminsky & HaussÜhl, 1990;Kudzin et al, 1994Kudzin et al, , 1995 attributed to the paraelectric to ferroelectric phase transition of LGO. The smallness of K pq and the applicability of relation (3) above only in a narrow range of temperature suggest that LGO may be an improper ferroelectric.…”

“…The dielectric constants were measured along the c-axis at the frequency of 1 MHz by means of a LCR meter (E7-12) in the temperature range from 298 K to 273 K (Bain, 1994;Kudzin et. al., 1994Kudzin et. al., , 1995.…”

“…A rather temperature hysteresis of impedance is observed in a cooling and heating cycle at T c = 283.5 K. The relative change of Δ|Z| (min) /|Z| (min) at the frequencies 100 kHz -10,000 kHz is shown in Like Fig.12, a similar kind of hysteresis was observed in the dielectric behavior of LGO, as described in section 2.1 and the appearance of the dielectric hysteresis is attributed to the internal space charge (electret state) effects which produce an internal electric field in LGO on heating from the ferroelectric phase. It was possible to compensate the internal electric field effects in dielectric measurements by an external electric field (Kudzin et al, 1994(Kudzin et al, , 1995Bain, 1994). It is suspected that the impedance (Z) hysteresis also occurs due to similar effects.…”