- EPR and optical study of Mn2+ doped ammonium oxalate monohydrate
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Studies on fine and hyperfine structures of paramagnetic resonance spectra in single crystals of Mn2+: ammonium oxalate monohydrate are reported. As sufficient numbers of lines were not obtained at room temperature, measurements have been done at liquid nitrogen temperature and at the frequency of X-band. The Mn2+ spin Hamiltonian parameters have been evaluated employing a large number of resonant line positions observed for various orientations of the external magnetic field and the surrounding crystalline field has been discussed. The values of the zero field parameters that give good fit to the observed EPR spectra have been evaluated. The values obtained for g, A, B, D, E and a are 2.0002±0.0002, (100±2)×10 -4, (79.5±2)×10-4, (257±2)×10-4, (85±2)×10-4 and (-18±1)×10-4 cm-1, respectively. The percentage of covalency of the metal-ligand bond is also determined. The optical absorption study has been done at room temperature. The observed bands are assigned as transitions from the 6A1g(S) ground state to various excited quartet levels of Mn2+ ion in a cubic crystalline field. The electron repulsion parameters (B and C), the crystal field splitting parameter(Dq) and the Trees correction (α) providing good fit to the observed optical spectra have been estimated and the values obtained for the parameters are B=897, C=2144, Dq=910 and α=76 cm-1.
- Kripal, Ram,Mishra, Vishal
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- Calorimetric study of phase transitions in ammonium hydrogen oxalate hemihydrate and its deuterated compound
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The molar heat capacities of ammonium hydrogen oxalate hemihydrate and its fully-deuterated compound were measured from 13 to 300 K. A higher-order phase transition was found in each compound. The temperatures and molar entropies of transition are 145.4K (6.01 J K-1 mol-1) and 160.1 K (8.23 J K-1 mol-1) in the protonated and deuterated compounds, respectively, where the mole refers to (NH4HC2O4)2·H2O or (ND4DC2O4)2·D2O. The entropies of the transitions indicate that they are order-disorder transitions, probably related to the ordering of one of the ammonium ions. The pressure coefficient of the transition temperature was calculated by the Ehrenfest relation and the available data of the thermal expansivity of the hydrogenous compound: -2.0 × 107 Pa K-1 in good agreement with a reported value -1.9 × 107 Pa K-1 based on a high pressure experiment.
- Fukai, Mari,Matsuo, Takasuke,Suga, Hiroshi
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p. 743 - 752
(2008/10/08)
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