Reversible structural change and thermodynamic properties of hydrogen in thin vanadium films

• The absorption of H in 50nm V(001) films under pressures of 1–104Pa H2 and at temperatures between 310 and 530K was studied using in situ combined x-ray diffraction (XRD) and electrical resistivity measurements. The H-induced XRD peak shifts clearly indicate a fully reversible and nondeteriorating first-order phase transformation for the film. The H-induced residual resistivity changes in the V film demonstrate several extreme points (maxima and minima) apparently associated with some special points on the pressure isotherms of the film both below and above the critical temperature (Tc=460±20K) . Correlating these extreme points with the known V(bulk)-H phase diagram indicates that, in addition to the first-order transformation, two additional reversible second-order transitions exist in the film. The enthalpy and entropy of this transformation, obtained from the temperature dependence of the plateau pressures, are ‑39±1kJ/mol°K , and ‑60±2J/mol , respectively. The thermodynamic constants and the lattice parameters of the phases for the first-order transformation in the film closely correspond to the α→β phase transformation in bulk V.

Subject headings

NATURVETENSKAP  -- Fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences (hsv//eng)

Keyword

Physics

Fysik

Publication and Content Type

ref (subject category)

art (subject category)