Chemistry for Sustainable Development 14 (2006) 395404 Phase State of YBa 2 Cu 3 O d d d d d (d d d d d = 6.77.4) That Has Been Modified at Ambient Temperature

Abstract The capability of YBa 2 Cu 3 O d for an intensive exchange with oxygen of a gas phase even at ambient temperature (t a ) that has been detected previously has been studied with diversified physical methods. An X-ray photoelectron spectroscopy method has been applied to demonstrate that a degree of ionicity of cation-oxygen bonds increases during oxidation under the t a conditions. Along with this phenomenon, oxygen appears in a state that is close to chemically unbonded. This correlates with evidence on spontaneous electric polarization that emerges in yttrium-baric cuprate under the test conditions. The obtained result has been explained in the context of YBa 2 Cu 3 O d model as of a virtual ferroelectric, the critical temperature of which in certain conditions can grow up to high positive values. In so doing, modification of chemical state of [BaO 2 ] structural group occurs from formal peroxide to formal oxide with strengthening of a certain BaO bond and with weakening of another one