Nuclear Resonance ofNb93in KNbO3

Abstract

The nuclear resonance of ${\mathrm{Nb}}^{93}$ in a single crystal of KNb${\mathrm{O}}_3$ has been studied in magnetic fields of approximately 5000, 100, and zero oersteds, and at temperatures between -196°C and +460°C. The quadrupole splitting of the magnetic resonance line in strong fields is found to be a sensitive function of crystal structure and, hence, of temperature. Temperatures of the phase transitions found in this way at about -50, +220, and +430°C are in agreement with other known data for this substance. The splitting $\Delta \nu$ of one satellite line is a continuous function of temperature between 220 and 430°C; near 430°C $\Delta \nu$ changes abruptly, indicating a first-order phase change. Below the Curie temperature (430°C) KNb${\mathrm{O}}_3$ is ferroelectric, with noncubic crystal structure. Above 430° it is cubic and a single resonance line is observed.