| Autor: |
Murgich, Juan, Abanero, Jose A., Santana R., Magaly, Capparelli, Mario V. |
| Předmět: |
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| Zdroj: |
Journal of Chemical Physics; 11/15/1986, Vol. 85 Issue 10, p6047, 7p |
| Abstrakt: |
14N nuclear quadrupole resonance (NQR) frequencies were measured between 77–328 K for simple monoclinic (1M) and orthorhombic (2Or) polytypes of potassium hexacyanoferrate (III) (KFR). A reversible first order transition was found at 133 K for 1M and at 138 K for 2Or polytype. The transition was interpreted in terms of the coupling of a quasisoft rotatory mode with a temperature dependent tilt motion of the complex ion. An irreversible interpolytype transition produced by internal strains was observed in a sample formed by 1M and 2Or polytypes and repeatedly cycled between around 80–140 K and room temperature. Selective broadening of lines observed in only a pair of N atoms of each hexacyanoferrate ion was attributed to the occurrence of one dimensional disorder of neighboring K ions. The disorder disappeared after sample recrystallization. It was found that low crystallization rates produced only the 1M structure while high rates increased the occurrence of the 2Or over 1M polytype and even produced a third polytype. Annealing of KFR for two weeks at 160 °C produced minor changes in polytypic composition thus showing a high energy barrier for interpolytypic conversion. The results obtained in KFR are explained in terms of the theory of order–disorder structures in layered compounds. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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