Phase transformation in HfPd observed through nuclear quadrupole interaction

The equiatomic alloy HfPd has been studied by perturbed angular correlation (PAC) spectroscopy using Hf-181 probe to observe its phase transformation with temperature. At room temperature, the martensitic phase of HfPd ((similar to)57%), Hf2Pd ((similar to)19%) and HfPd2 ((similar to)24%) have been found. At a slightly higher temperature (373 K and above), no phase of HfPd2 is observed but, both martensitic and cubic austenite phases of HfPd are found. The phase Hf2Pd is present in the whole temperature range. Up to 573 K, the cubic austenite phase of HfPd is found to increase with temperature at the expense of martensitic HfPd phase. At 673 K, the phase Hf2Pd increases abruptly and remains same in the temperature range 673-973 K ((similar to)30%). The cubic HfPd phase remains almost unchanged in this temperature range ((similar to)38%). From present measurements, beginning of phase transformation from martensitic to austenite is found at a much lower temperature of 373 K. In the temperature range 373-973 K, both martensitic and austenite phases of HfPd coexist while from previous measurements by differential scanning calorimetry, the cubic austenite to martensitic phase transformation was found at about 823 K. XRD measurements at room temperature have also been carried out to identify the different phases of Hf-Pd. The new Hf2Pd3 phase of Hf-Pd system that was reported by a sole group has been confirmed from present powder XRD pattern in annealed sample.