The literature review based on the works published over the last decade concerns the progress in research on innovative piezoelectric materials with current or potential practical applications. At the beginning, the nature of piezoelectric phenomenon is clarified. The main emphasis is put on presentation of polymers, biopolymers and polymer composites as well as hybrid materials with piezoelectric properties. Moreover, carbon nanomaterials are also included. These materials have recently become an intensively developing field, as evidenced by numerous scientific publications. Furthermore, the recently reported main methods of characterizations and selected examples of modern applications of piezoelectric materials in various fields (electronics, industry, medicine) have been discussed. The bibliography includes 217 references.

Polymeric cellular composites are very important materials in modern electronics because they can be used as piezopolymers due to low specific weight, good thermal resistance and high value of piezoelectric constant d₃₃. The aim of this work was to obtain and characterize the cellular polypropylene (PP) composites as materials designed for microelectronics. PP has been modified by addition of commercial silicate filler and the obtained materials were extruded. Then, the composites were subjected to electric field for polarization. Effect of the filler content on the structure and physicochemical properties of the composites have been investigated. The following experimental methods have been applied: SEM, XRD, thermogravimetry, tensile tests and measurements of voltage and electric charge accumulated in the polymer. The piezoelectric constant and stability of piezoelectric properties were also determined. It was found that the growth in the filler content in the polymer causes the increase in the film porosity and the degree of PP crystallinity that reaches 70% for the PP sample with 10% of the filler. Young’s modulus increased also in the presence of the filler. Moreover, the thermal stability of the composites was improved compared to neat PP. The piezoelectric constant of the composites was about 200 pC/N).

The development, universality and miniaturization of electronic devices leads to the search for new piezoelectric materials, among which recently, polymers play an increasingly important role. In this work, composites based on two types of polyethylene—high density polyethylene (HDPE), and medium density polyethylene (MDPE)—and aluminosilicate fillers were obtained by extrusion process. This method allowed obtaining flexible electrets in the form of a thin film after polarization under a constant electric field of 100 V/μm. The morphology of the composites was characterized by scanning electron microscopy, whereas the crystallinity was determined by X-ray diffraction. The mechanical properties and thermal stability of the composites were examined by means of tensile tests and thermogravimetry, respectively. The piezoelectric characteristics were appointed by measuring the electric charge and the voltage in the polarized samples. Piezoelectric coefficients, and the stability of electrets over time were also determined. Moreover, the effect of film orientation on piezoelectric properties was investigated. Composites with appropriate morphology (i.e., well dispersed filler particles in the polymer matrix and formed holes) were obtained which ensured permanent electrical polarization. It was found that the best piezoelectric, mechanical properties and thermal stability exhibits HDPE composite with 5% of aluminosilicate filler.

PP-based composites with two mineral fillers (perlite or glass beads) were manufactured by extrusion, and then subjected to orientation in a ratio of 3:1. Electrets were obtained in the polarization process under the influence of a constant electric field. Sample morphology was tested by SEM whereas the crystallinity was determined by XRD. Mechanical strength and thermal stability of composites was studied by tensile tests and thermogravimetric analysis, respectively. The piezoelectric characteristics were appointed by measurement of the electrical charge and current voltage in the polarized samples. The dependence of thermally stimulated depolarized current (TSDC) on temperature was also investigated. The piezoelectric coefficient (d₃₃), the electret stability over time as well as activation energy of depolarization process have been determined. It was found that low filler content (i.e. 2.5 and 5 wt.% of glass beads and perlite, respectively) significantly improve piezoelectric properties of isotactic polypropylene (i-PP).

Isotactic-polypropylene (i-PP) films with inorganic minerals such as Sillikolloid, perlite, or glass beads were prepared. The obtained polymeric films were subjected to an orientation process. Moreover, this paper includes results how the artificial accelerated weathering influences surface properties of the unoriented and oriented i-PP films with the mineral fillers. Changes in the ultraviolet (UV) treated polymeric films were studied with attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and by measuring contact angles. The results revealed that photooxidation of i-PP was more effective in the presence of the fillers and depended on the type of the filler but not on its amount. Moreover, the oriented samples experienced more effective photooxidation compared with the unoriented ones. In all studied samples the same photoproducts were detected, suggesting the same route of polymer photooxidation with and without the filler. These polymeric films were produced for potential applications in the devices in which piezoelectric effect can be used.