An electron spin-resonance study of CIO3 radicals in NH4 CIO4 single crystals

Hegde, B. G. ; Rastogi, Amit ; Damle, R. ; Chandramani, R. ; Bhat, S. V. (1997) An electron spin-resonance study of CIO3 radicals in NH4 CIO4 single crystals Journal of Physics: Condensed Matter, 9 (15). ISSN 0953-8984

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An ESR study ofCIO3 centres in x-irradiated ammonium perchlorate(NH4CIO4) single crystals is carried out that is aimed at resolving the controversy that has recently arisen over the possible occurrence of low-temperature phase transitions in the compound (room temperature structure: orthorhombic; space group Pnma). The ESR spectra are recorded as a function of the orientation of the magnetic field H in the three orthogonal crystallographic planes at 300 K, 77 K, and 4.2 K, and also as a function of temperature for H parallel to the principal z-component AZZ(Cl) of the 35 Cl hyperfine coupling tensor. The analysis of the spectra shows that while the g-tensor remained axial over the entire temperature range(g=2.0052(3), 2.0055(3), 2.0057(3) and g =2.0090(3), 2.0096(3), 2.0105(3) at 300 K, 77 K, and 4.2 K respectively), A (Cl), which is rhombic at room temperature (AZZ=429.77 (1.0) MHz,Ayy = 316.15 (1.0) MHz and Axx = 325.98 (1.0) MHz, at 300 K) becomes more axial as the temperature is lowered Azz= 441.90 (1.0) MHz Ayy=299.09 (1.0) MHz and Axx = 301.61(1.0) MHz at 77 K, and A yy = 303.43 (1.0) MHz at 4.2K). No changes in the spectra attributable to any phase transition were observed, and we conclude that NH4CIO4does not undergo any phase transition below room temperature. Furthermore, it is found that duringCl04' CIO3 radiative decomposition the mirror-related Cl - O bonds, even though weaker than the other Cl - O bonds, do not break, thus confirming our earlier conclusion that mirror symmetry is preserved during radiation damage.

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Deposited On:09 Oct 2010 05:46
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