87Rb NMR study at the cubic to tetragonal phase transition in RbCaF 3

Abstract

The 87Rb nuclear magnetic resonance spectrum, in perovskite single crystal of RbCaF3, is studied above and below the cubic-to-tetragonal phase transition occurring at 198 K. In the high-temperature cubic phase, the temperature dependence of the resonance line amplitude deviates from the Curie law and this can be attributed to the existence of tetragonal domains. In the low temperature tetragonal phase, a second-order quadrupole shift of the central line is observed, from which the CaF6 tilt angle (order parameter) is derived. The order parameter temperature dependence is described by a power law with a cross over from exponent 0.5 to exponent 0.32 at 150 K. The tilt angle Φ is compared to the values obtained from X-ray and neutron powder diffraction data.