Dielectric studies of lanthanum heptamolybdate crystals grown from gels

✍ Scribed by Sushma Bhat; S.K. Khosa; P.N. Kotru; R.P. Tandon

• Book ID: 103954435
• Publisher: Elsevier Science
• Year: 1995
• Tongue: English
• Weight: 378 KB
• Volume: 30
• Category: Article
• ISSN: 0921-5107
• DOI: 10.1016/0921-5107(94)01129-x

✦ Synopsis

Results of dielectric measurements conducted on lanthanum heptamolybdate grown by a gel technique employing the system La(NO3)3-MoO3-NH4OH-HNO3-Na2SiO 3 are presented. The variations of the dielectric constant e', dielectric loss tan6 and conductivity o with the temperature and frequency are critically analyzed. The dielectric constant increases with temperature at lower frequencies (103 Hz), reaching a maximum value of 320 at 125 °C, after which it abruptly decreases. The dielectric loss tan 6 and conductivity o 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 C r= a0+ a I T 2

-lno=a+ b(T-To) 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 being ferroelectric.