Dielectrics and possible ferroelectricity in diol/glycerol covalently grafted kaolinites

Kaolinite possesses a structure with asymmetrically layered 1 : 1 dioctahedral aluminum silicate, and this structural property provides a useful platform for creating new cost-efficient functional materials that require noncentrosymmetric crystal packing. In this study, we prepared three covalently grafted kaolinites of propanediol (PD)/butanediol (BD)/glycerol (GL) by forming Al-O-C bonds between the OH groups of PD/BD/GL and the surface of kaolinite (K). Three covalently grafted kaolinites (K-PD, K-BD and K-GL) were characterized by X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy and microanalysis for C, H and N elements. The test of K-PD, K-BD and K-GL stirred with water at ambient conditions for 3 days demonstrated these hybrids showing extra high chemical stability to water. The dielectric spectra of three hybrids show two-step dielectric relaxation in the range of 1-10⁷ Hz, and the P-E measurements revealed the existence of ferroelectricity at room temperature with the spontaneous polarization, the remanent polarization and the coercive field of ∼0.014 μC cm^-2, ∼0.008 μC cm^-2 and ∼0.426 kV cm^-1 for K-PD, ∼0.017 μC cm^-2, ∼0.011 μC cm^-2 and ∼0.645 kV cm^-1 for K-BD, and ∼0.018 μC cm^-2, ∼0.011 μC cm^-2 and ∼0.141 kV cm^-1 for K-GL, respectively.