The perturbed angular correlation method was employed to study the
temperature dependence of electric field gradients at the 181Ta probe in the
polycrystalline Hf2Ni7 compound. The temperature evolution of the sample
content was measured using high-temperature X-ray diffraction. To check the
magnetic order of the sample, magnetization measurements and additional
perturbed angular correlation measurements with externally applied magnetic
field were performed. All obtained spectra showed no evidence of magnetic
order of the Hf2Ni7 phase. Within the experimental resolution of the
apparatus, the measured electric field gradients at 181Ta probe for the two
inequivalent 181Hf/181Ta sites in the Hf2Ni7 compound appeared as one in the
range of 78-944 K. A single quadrupole interaction implies that the electric
field gradients at the two Hf sites must be quite similar. At 293 K, the
measured quadrupole interaction parameters are ?Q = 433(1) MHz and ? =
0.300(4). An increase of the quadrupole frequency and a gradual rising of the
asymmetry parameter were observed with increasing temperature. The
high-temperature X-ray diffraction indicated a build up of HfO2 above 693 K.
Electric field gradients in Zr8Ni21 and Hf8Ni21 intermetallic compounds; results from perturbed angular correlation measurements and first-principles density functional theory
