High-precision P-31 chemical shift measurements on KH2PO4-type crystals: role of electronic instability in the ferroelectric transition mechanism

The mechanism of the ferroelectric transition in KH2PO4-type crystals has b een probed using magic angle spinning P-31 NMR on single crystals. The high er resolution thus obtained has enabled us to detect a marked change in the 31P isotropic chemical shift around the transition temperature T-c, with a clear jump at T-c. These results are interpreted as evidence that the tran sition involves a displacive component with electronic instabilities playin g a role in the driving mechanism.