Second order phase transition of Al(urea)6(ClO4)3 as observed from esr measurements of Cr(urea)6(ClO4)3 in Al(urea) 6(ClO4)3

✍ Scribed by J.H.M. Mooy; H.J. de Jong; M. Glasbeek; J.D.W. van Voorst

• Publisher: Elsevier Science
• Year: 1973
• Tongue: English
• Weight: 332 KB
• Volume: 18
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(73)80336-7

✦ Synopsis

Electron spin resonance of aluminum hesaurcn perchlorate doped with Cr(urca),&C104)~ has been investigated in the temperature range 77 io 360°K. At 77°K the vaiucs of the spin hnmiitonian paramctcrs of the chromium complex are: IDI = (168 2 10) X lo4 cm -I, IEI = (t62k 10) X lo4 cm-',gli = 1.977 2 O.OOl,g,= 1.975 + O.OCl and D/E > 0. The temperature dependence of these parameters indicates that the crystal undergoes a second order phase transition at T, = (295 ? l)"K. In the proposed model the phase transition is triggered by an ordering in 'he orientation of the oxygen atoms in the perchlorate ions, half of which arc assumed to be disordered a; temperatures above Tc.