The charge states in polypropylene doped with ZrO2 nanoparticles and their changes at heat treatmentHijran S. Ibrahimova and Tahir D. IbragimovEur. Phys. J. B, 97 10 (2024) 158DOI: https://doi.org/10.1140/epjb/s10051-024-00801-5