Dielectric relaxation and alternating current conductivity of polyvinylidene fluoride doped with lanthanum chloride

Abstract

X-ray diffraction (XRD), dielectric constant (ɛ′), dielectric loss factor (ɛ″), and ac conductivity (σac) of pure and LaCl3-doped polyvinylidene fluoride (PVDF) have been carried out. The dielectric properties have been studied in the temperature and frequency ranges; 140–450 K and 0.1−1000 kHz, respectively. XRD results reveal that pure and LaCl3-PVDF samples are in the α-phase. The incorporation of La3+ ions within the PVDF polymer matrix forms complexes which reduce the order structure of PVDF. Three relaxation processes, namely; ρ, αa, and αc were observed for pure PVDF. The first relaxation can be explained based on space charge formation or Maxwell-Wagner polarization. The second one occurs around the glass transition temperature, Tg, and is related to the micro-Brownian motion of the main polymer chain. It becomes broad and shifted to higher temperatures with the doping of LaCl3. The third process appears below the melting temperature of PVDF and can be attributed to molecular motions of the main polymer chain. The behavior of the ac conductivity shows that the conduction mechanism of pure, 5 wt. % and 10 wt. % of LaCl3-doped PVDF samples is follows the correlated barrier hopping (CBH) model, while 3 wt. % of LaCl3-doped PVDF exhibits a small polaron tunneling (SPT) conduction.