The valence state of bismuth in BaBiO3 probed by NQR

We report the NQR on Ba nuclei in four samples of BaBiO3 prepared in differ ent ways. The spectra of Ba-137 consist of broad line centered near 18 MHz at 4.2 K. The broadening of NQR suggests a local distortions of the crystal structure. The area under the line for ceramic sample BaBiO3 synthesized a t 800 degreesC is approximately two times larger comparing to ceramic sampl es and single crystal prepared at 930-1080 degreesC. The decrease of the NQ R signal is attributed to the partial disordering of charge disproportionat ing Bi ions on the two inequivalent sites.