Non-equivalence of Cu crystal sites in CuGeO3 as evidenced by NQR

Nuclear quadrupole resonance results on the inorganic spin-Peierls compound CuGeO3 were re-examined using a single crystal and enhanced resolution. A clear splitting of (CU)-C-63,65 NQR lines of about 250 kHz at 4.2 K was obs erved. Such a splitting has not been previously seen in Cu NQR spectra meas ured on polycrystalline samples of CuGeO3 (Itoh M et al 1995 Phys. Rev. B 5 2 3410, Kikuchi et al 1994 J. Phys. Sec. Japan 63 872). The mean frequency of the Cu doublet is in agreement with the Cu NQR frequency observed on pow der samples. The splitting does nor disappear with increasing temperature a bove T-sP exhibiting only a slight kink at around 16 K. This points to a no n-magnetic origin of the splitting which can be attributed to existence of at least two non-equivalent Cu crystal sites in CuGeO3 structure, as predic ted by precise x-ray study and EPR measurements (Hidaka M et al 1997 J. Phy s.: Condens. Matter 9 809, Yamada I er al 1996 J. Phys.: Condens. Matter 8 2625).