Effect of pressure on the lattice distortion of indium to 56 GPa

The change in the axial radio c/a of indium has been precisely determined under pressures up to 56 GPa at room temperature. The high-pressure powder-x-ray-diffraction techniques utilize an imaging plate and a synchrotron-radiation source. The axial ratio of the face-centered tetragonal lattice increases with pressure from the value at atmospheric pressure (c/a=1.0757), reaching a maximum of 1.091 around 24 GPa (V/V₀=0.75) and decreases with further compression. The bulk modulus and its pressure derivative have been determined as B₀=41.8±{}0.5 GPa and B₀^'=4.81±{}0.06, respectively. The present result differs considerably from the previous measurements, in which a maximum in c/a was observed at pressures lower than 10 GPa. The origin of (c/a)ₘₐₓ has been discussed in terms of the pseudopotential of indium under pressure.