Supposing the presence of a doping-induced narrow band besides the valence band, the vibronic dynamic instability caused by interaction of these bands is analysed having in mind the description of the recently observed d 0X05 structural transformation in YBa 2 Cu 3 O 7Àd .Various structural events on bulk, mesoscopic and local scales are known in high-T c superconductors. Distinct doping treatments are necessary to reach high T c values, which influence also the structural properties. The charge carriers (holes) created by doping lead to the formation of polaron-type clusters with phase separation [1,2,3,4,5]. A striped structure of the superconductivity play-ground CuO 2 planes has been found [4,5,6,7,8]. Distorted material (LTT structure) stripes of mesoscopic size intercalate undistorted (LTO) bulk bearing itinerant carriers. In the distorted region the plane Cu (2) is shifted towards the apex O(4) ion. These structural data support the two-component scenario of the high-T c superconductivity [9,10,11,12] incorporating itinerant and localized (polaron) type carriers. Such approaches are developing in various realizations at present and take account of changes in the electron spectrum due to the doping. At favourable for the high T c compositions the actual part of the electronic spectrum seems to consist of a wide valence hole band and an outpushed narrow band created through hole capture and lattice distortion [9,12,13,14]. Interband pair-scattering superconductivity [15] in such a two-band model has been considered in [16].The presence of two sufficiently close electron bands opens a structural instability channel through their vibronic mixing [17] (like a band-pseudo-Jahn-Teller-effect). Such a scheme has been used to describe the T-O displacive structural transition in La 2Àx Sr xCuO 4 [18]. Recently a displacive structural transformation in the CuO 2 planes of YBa 2 -Cu 3 O 7Àd at d 0X05 and T 25 K has been found [19]. It consists in dominant and anomalously large displacement of the Cu(2) ion off the O(2, 3) layer. This d value corresponds to the under-overdoped phase separation line. One can expect that under such conditions the polaron-like narrow induced band has a ripe development. The structural transition under consideration has seemingly relations to doping-induced stripening of the CuO 2 plane, phase separation and modification of the electronic spectrum.We try to associate the d 0X05 transition with the vibronic interaction between the wide-valence (predominantly O2p) and hole-induced narrow band. The energy zero is taken at the bottom of the wide band