Dielectric studies of lanthanum heptamolybdate crystals grown from gels

TLDR: In this paper, the variations of the dielectric constant, the loss tan and the conductivity with the temperature and frequency are analyzed, and the functional relationship between the different values of these values is determined by fitting the observed data with the respective polymeric expressions of the type ϵ ′ = a 0 + a 1 T 2 - lnσ = a + b (T - T 0 ) 2.

Abstract: Results of dielectric measurements conducted on lanthanum heptamolybdate grown by a gel technique employing the system La(NO 3 ) 3 MoO 3 NH 4 OHHNO 3 Na 2 SiO 3 are presented. The variations of the dielectric constant e′, dielectric loss tan δ and conductivity σ with the temperature and frequency are critically analyzed. The dielectric constant increases with temperature at lower frequencies (10 3 Hz), reaching a maximum value of 320 at 125 °C, after which it abruptly decreases. The dielectric loss tan δ and conductivity σ show both a temperature as well as a frequency dependence. The sharp increase in e′ with temperature is attributed to total polarization resulting from a space charge effect. The functional relationship between the dielectric constant, conductivity and temperature is determined by fitting the observed data with the respective polymeric expressions of the type ϵ ′ = a 0 + a 1 T 2 - lnσ = a + b ( T - T 0 ) 2 The non-linearities and anomalous behaviour of the dielectric constant near the transition temperature, supported by hysteresis studies, indicate the possibility of these materials ferroelectric.