A perturbed angular correlation spectrometer for material science studies

Journal of Alloys and Compounds

Saha

et al. 2017

Time-differential perturbed angular correlation (TDPAC) measurements have been carried out in stoichiometric ZrNi 3 and HfNi 3 intermetallic compounds using 181 Ta probe in the temperature range 77-1073 K considering the immense technological applications of Zr-Ni and Hf-Ni intermetallic compounds. In ZrNi 3 , four components due to the production of Zr 2 Ni 7 , Zr 8 Ni 21 , Zr 7 Ni 10 and ZrNi 3 have been found at room temperature. The HfNi 3 sample produces five electric quadrupole interaction frequencies at room temperature. The phase HfNi 3 is strongly produced in stoichiometric sample of HfNi 3 where two non-equivalent Hf sites are found to be present. Besides this phase, two other phases due to Hf 2 Ni 7 and Hf 8 Ni 21 have been found but, we do not observe any phase due to Hf 7 Ni 10 . X-ray diffraction, TEM/energy dispersive X-ray spectroscopy (EDX) and TEM-selected area electron diffraction (SAED) measurements were used to further characterize the investigated materials and it was found that these results agree with the TDPAC results. In order to confirm findings from TDPAC measurements, density functional theory (DFT) based calculations of electric field gradients (EFG) and asymmetry parameters at the sites of 181 Ta probe nucleus were performed. Our calculated results are found to be in excellent agreement with the experimental results.

Section: Methodsmentioning

confidence: 99%

Identification of phase components in Zr-Ni and Hf-Ni intermetallic compounds; investigations by perturbed angular correlation spectroscopy and first principles calculations

Journal of Alloys and Compounds

Saha

et al. 2017

“…The defination of S kn coefficients can be found in ref. 34 . Due to chemical inhomogeniety in the sample, all probe nuclei do not experience exactly the same EFG but slightly different EFG’s are experienced which produces a distribution of frequency around the principle value and this gives rise to a broadening of frequency.…”

Section: Methodsmentioning

confidence: 99%

“…Here, W 13 (180°, t ) is the random subtracted coincidence count for the detector combination of 1 and 3 set at an angle 180° at time channel t. Neglecting A 44 (A 22 ≫ A 44 ), the A 22 G 22 ( t ) can be found from R(t) as 34 …”

Section: Methodsmentioning

confidence: 99%

Martensitic phase transformation in TiNi

Sewak

2019

Sci Rep

Self Cite

From temperature dependent perturbed angular correlation (PAC) measurements (77–873 K) in equiatomic TiNi intermetallic alloy, martensitic phase transformations have been observed. Three frequency components corresponding to three different phases of TiNi have been found in the temperature range 298–873 K. The results of quadrupole frequency and asymmetry parameters at room temperature are found to be: ωQ = 14(1) Mrad/s, η = 0 (33%), ωQ = 40.0(5) Mrad/s, η = 0.66(3) (52%) and ωQ = 56.7(3)Mrad/s, η = 0.39(2) (15%). The frequency component with η = 0 and which enhances to ~52% at 373 K can be attributed to the cubic austenite phase. The predominant component (~52%) found at room temperature has been attributed to monoclinic martensitic phase of TiNi and the third component with values of ωQ and η similar to those for the martensitic phase is attributed to the intermediate orthorhombic phase. At 77 K, no intermediate and austenite phases have been found but only the martensite phase is observed at this temperature. From XRD measurements at room temperature also, three phases of TiNi have been observed.

“…For TD-PAC measurements, a four detector spectrometer with BaF 2 detectors has been used. From the four coincidence spectra (two at 180 • and two at 90 • ), the perturbation function G 2 (t) has been found as described earlier [13]. For measurement above room temperature, a small resistive furnace has been used.…”

Section: Methodsmentioning

confidence: 99%

Oxidation of Hafnium and Diffusion of Hafnium Atoms in Hexagonal Close-Packed Hafnium; Microscopic Investigations by Perturbed Angular Correlations

Zeitschrift Für Naturforschung A

2012

Time-differential perturbed angular correlation (TDPAC) studies in hafnium metal (∼ 5% Zr) have been carried out at different temperatures. It is found that hafnium metal on heating at 873 K continuously for two days in air, transforms partially and abruptly to HfO 2 while no component of oxide has been observed for heating up to 773 K and during initial heating at 873 K for 1 day. This result is strikingly different to that expected from the Arrhenius theory. Also, a strong nuclear relaxation effect has been observed at 873 K due to rapid fluctuation of hafnium atoms in hexagonal closepacked (hcp) hafnium. At this temperature, ∼ 45% probe nuclei experience static perturbation due to monoclinic HfO 2 , ∼ 50% experience fluctuating interaction, and ∼ 5% produce static defect configuration of hcp hafnium. With lowering of temperature, defect configurations of hafnium increase at the cost of fluctuating interaction. An almost total fluctuating interaction observed in hcp hafnium at a temperature much lower than its melting point is another interesting phenomenon.