Crystalline phases in Zr9Ni11 and Hf9Ni11 intermetallics; Investigations by perturbed angular correlation spectroscopy and ab initio calculations

Crystalline phases formed in stoichiometric Zr${}_9$Ni${}_{11}$ and Hf${}_9$Ni${}_{11}$ have been studied by perturbed angular correlation (PAC) spectroscopy, XRD and TEM/SAED measurements. In Zr${}_9$Ni${}_{11}$, the phases Zr${}_9$Ni${}_{11}$ ($\sim$89%) and Zr${}_8$Ni${}_{21}$ ($\sim$11%) have been found at room temperature from PAC measurements. At 773 K, Zr${}_9$Ni${}_{11}$ partially decomposes to Zr${}_7$Ni${}_{10}$ and at 973 K, it is completely decomposed to ZrNi and Zr${}_7$Ni${}_{10}$. In Hf${}_9$Ni${}_{11}$, a predominant phase ($\sim$81%) due to HfNi is found at room temperature while the phase Hf${}_9$Ni${}_{11}$ is produced as a minor phase ($\sim$19%). No compositional phase change at higher temperature is found in Hf${}_9$Ni${}_{11}$. Phase components found from XRD and TEM/SAED measurements are similar to those observed from PAC measurements. Electric field gradients in Zr${}_9$Ni${}_{11}$ and Hf${}_9$Ni${}_{11}$ have been calculated by density functional theory (DFT) using all electron full potential (linearized) augmented plane wave plus local orbitals [FP-(L)APW+lo] method in order to assign the phase components.