Hydrostatic contraction and anisotropic contraction effects on oxygen molecule nanorods

We study the effects of both hydrostatic and anisotropic contractions on the molecular condensation of oxygen molecules (O2) physisorbed to nanosized pores, termed “O2 nanorods”, through the magnetization measurements. Multisteps of O2 solidification accompany the reduction in structural symmetry with decreasing temperature, such that the structural change by external stress varies the stability of O2 solidification. For initial pore diameters of D = 8.5, 14.5, and 24.0 nm, anisotropic compression for nanorods (preferential compression along radial direction of the pores) occurred, and molecule solidification is suppressed at the lower temperature side compared with that under hydrostatic compression. For the smallest D = 6.5 nm, a hydrostatic contraction almost occurred, and the high adsorption capability enabled the detection of both the melting transition and change in crystal structure within the β phase, in addition to α–β and β–γ transitions.