Study of ferroelectric phase transitions by electric field perturbation of nuclear quadrupole resonance spectra

Theoretical aspects of electrically induced shifts of nuclear quadrupole resonance spectra are considered at ferroelectric phase transitions. The displacive and order-disorder types of phase transitions are analysed. Calculations and experimental data for the low-temperature phase transition in pyrargyrite (Ag ₃SbS ₃ show good agreement. It is confirmed that the above phase transition is of the order-disorder type. The phase transition is shown to be connected with the ordering of the silver ions in the double-minimum potential of the ionic bond S-Ag-S.