Dielectric spectroscopy, ferroelectrics

J. Grigas, Microwave Dielectrics spectroscopy of Ferroelectrics and Related Materials, Gordon and Beach Publishers, 1996. 

The molecular origin of ferroelectricity in FLCs is attributed to a pronounced anisotropy of the angular orientations of the lateral dipole moments, induced by the tilt of the molecular long axes with respect to the normal of the smectic layers. This is supported by the results of broadband dielectric spectroscopy performed on a low molecu-... 

Additional information on ferroelectric and electroclinic switching can be obtained with broadband dielectric spectroscopy. It appears that the molecular dynamics of FLCPs are comparable to those of low molecular weight compounds [67]. However, the experimental observations are made more difficult for FLCPs than for low molecular weight SmC liquid crystals due to the conductivity contribution which takes place at frequencies below 10" Hz and to the difficulty to get a macroscopically well-aligned sample. 

A full control of processing and the clarification of new and complex physical phenomena clearly require improved structural and mechanical analyses, among which CL spectroscopy offers the smallest available probe size. CL technique has been found to be highly versatile for comprehensive analyses of a wide range of ceramic oxides, including dielectrics and ferroelectrics [13,14]. This technique allows one to evaluate defect structures with high (from sub-micrometer to nano-meter scale) spatial resolution. 

Kremer, E. (1997), Broadband dielectric spectroscopy on collective and molecular dynamics in ferroelectric liquid crystals, in Dielectric Spectroscopy of Polymeric Materials—Eundamental and Applications, Runt, J. P. and Eitzgerald, J. J., eds., ACS, Washington, DC, pp. 423 44. 

Bias-induced reverse piezoelectric response Broadband dielectric spectroscopy (BDS) Dielectric permittivity spectrum Dielectric resonance spectroscopy Elastic modulus Ferroelectrets Electrical breakdown Acoustic method Characterization Dynamic coefficient Interferometric method Pressure and frequency dependence of piezoelectric coefficient Profilometer Quasistatic piezoelectric coefficient Stress-strain curves Thermal stability of piezoelectricity Ferroelectric hysteresis Impedance spectroscopy Laser-induced pressure pulse Layer-structure model of ferroelectret Low-field dielectric spectroscopy Nonlinear dielectric spectroscopy Piezoelectrically generated pressure step technique (PPS) Pyroelectric current spectrum Pyroelectric microscopy Pyroelectricity Quasistatic method Scale transform method Scanning pyroelectric microscopy (SPEM) Thermal step teehnique Thermal wave technique Thermal-pulse method Weibull distribution... 

The particular choice of the authors was rather to put emphasis on experimental techniques that are either specifically relevant or powerfiil with respect to ferroelectric polymers and fenoelectrets or represent recent experimental developments and trends. In this sense, room was given to nonlinear dielectric properties that can be probed by nonlinear dielectric spectroscopy and various types of hysteresis experiments. Besides a systematic description of piezoelectric and inverse piezoelectric techniques, we have added dielectric resonance spectroscopy as an all-round approach yielding elastic, piezoelectric, and dielectric properties of polymer electrets in a single dielectric measurement. 

Ultraviolet Raman spectroscopy has emerged as a powerful technique for characterization of nanoscale materials, in particular, wide-bandgap semiconductors and dielectrics. The advantages of ultraviolet excitation for Raman measurements of ferroelectric thin films and heterostructures, such as reduced penetration depth and enhanced scattering intensity, are discussed. Recent results of application of ultraviolet Raman spectroscopy for studies of the lattice dynamics and phase transitions in nanoscale ferroelectric structures, such as superlattices based on BaTiOs, SrTiOs, and CaTiOs, as well as ultrathin films of BaTiOs and SrTi03 are reviewed. 

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