The microscopic origin of the pyroelectric power generation using ferroelectric ceramics for energy harvesting from time-varying waste heat can be understood by conducting operando neutron diffraction measurements. The behavior of the domain orientation and lattice strain in the lead zirconatetitanate-based ceramics with a tetragonal structure during the novel power generation cycle combining the electric field and the temperature change were investigated. The [001] domains and the lattice strain of the (111) plane in the direction parallel to the electric field increase in the process of simultaneous rise in the electric field and temperature and rapidly decrease in the process of the field drop. Furthermore, larger structural changes were found in the material and cycle condition, giving higher power density. The alignment of the domain orientation by the electric field and its randomization by the higher temperature during the cycle are critical features of the current power generation system. Published under an exclusive license by AIP Publishing.& nbsp;