An electron spin-resonance study of $ClO_3$ radicals in $NH_4$$ClO_4$ single crystals

Hegde, BG and Rastogi, A and Damle, R and Chandramani, R and Bhat, SV (1997) An electron spin-resonance study of $ClO_3$ radicals in $NH_4$$ClO_4$ single crystals. In: Journal Of Physics and Condensed Matter, 9 (15). pp. 3219-3226.

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Abstract

An ESR study of ClO3 centres in x-irradiated ammonium perchlorate (NH4ClO4) 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 A(zz)(Cl) of the Cl-35 hyperfine coupling tenser. The analysis of the spectra shows that while the g-tensor remained axial over the entire temperature range (g(parallel to) = 2.0052(3), 2.0055(3), 2.0057(3) and g(perpendicular to) = 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 (A(zz) = 429.77(1.0) MHz, A(yy) = 316.15(1.0) MHz, and A(xx) = 325.98(1.0) MHz at 300 K) becomes more axial as the temperature is lowered (A(zz) = 441.90(1.0) MHz, A(yy) = 299.09(1.0) MHz, and A(xx) = 301.61(1.0) MHz at 77 K, and A(zz) = 445.55(1.0) MHz, A(yy) = 299.84(1.0) MHz, and A(xx) = 303.43(1.0) MHz at 4.2 K). No changes in the spectra attributable to any phase transition were observed, and we conclude that NH4ClO4 does not undergo any phase transition below room temperature. Furthermore, it is found that during ClO4- --> ClO3 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.

Item Type:	Journal Article
Publication:	Journal Of Physics and Condensed Matter
Publisher:	Institute of Physics
Additional Information:	Copyright of this article belongs to Institute of Physics.
Department/Centre:	Division of Physical & Mathematical Sciences > Physics
Date Deposited:	03 Jun 2009 04:58
Last Modified:	19 Sep 2010 05:01
URI:	http://eprints.iisc.ac.in/id/eprint/18325

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