NEUTRON-SCATTERING STUDIES OF INPLANE ZONE BOUNDARY PHONONS OF YBA2CU3O6.6 (T(C)SIMILAR-OR-EQUAL-TO-53-K) AND YBA2CU3O6.9 (T(C)SIMILAR-OR-EQUAL-TO-90-K)

Energies of several in-plane phonons have been measured as a function of temperature T up to about 500 K in the highest case, for crystals of YBa2Cu3O6.6 (T(c) congruent-to 53 K) and YBa2Cu3O6.9 (T(c) congruent-to 90 K), in which the magnitudes of the transport anomalies are very much different. For a phonon mode in the rather narrow q-region near the zone boundary, or for a mode well characterized by the dimerization type motion of nearest neighbor Cu atoms in the CuO2 planes, the T-dependence of the phonon-energy is larger for the former crystal than the latter one, suggesting that the T-dependence is stronger for samples with larger transport anomalies.