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- Title
A New Polymorph of Potassium Chromate(III), β-KCrO<sub>2</sub>, and Reinvestigation of α-KCrO<sub>2</sub>.
- Authors
Zafar Ali, Naveed; Nuss, Jürgen; Jansen, Martin
- Abstract
α-KCrO2 was synthesized by the azide/nitrate route. Stoichiometric mixtures of the precursors (KN3, KNO3, and Cr2O3) were heated in a special regime up to 853 K and annealed at this temperature for 5 h in a specially designed silver container. Dark green single crystals of β-KCrO2 were grown by post annealing the reaction product at 773 K for 200 h in silver crucibles. According to single-crystal X-ray analysis, the new high temperature modification, β-KCrO2, crystallizes in the β-RbScO2 type of structure [ P63/ mmc; a = 3.0427(4) Å, c = 11.924(2) Å; c/ a = 3.918; Z = 2]. The characteristic feature of the structure are CdCl2 analogue slabs of [CrO6/3]- edge shared octahedra stacked along the [001] direction with K+ atoms incorporated between the layers in a trigonal prismatic arrangement, rare for lighter alkali atoms. We have reinvestigated the specific heat (from 2 to 300 K) and the magnetic susceptibility (2 to 350 K) on α-KCrO2, and clearly identified in the specific heat measurements, a λ-type anomaly at 23 K, indicating the onset of long-range AFM ordering. The Curie-Weiss fit of experimental data in the temperature range above 100 K, yields the negative Curie-Weiss temperature of -220 K, indicating predominant antiferromagnetic spin-exchange interaction, with an effective magnetic moment ( μeff) of the order of 3.91 μB, corresponding to a g-factor [ μeff /μB = g[ S( S+1)]1/2] of 2.019 well in accordance for Cr3+ ( d3 system) with spin S = 3/2.
- Publication
Zeitschrift für Anorganische und Allgemeine Chemie, 2013, Vol 639, Issue 2, p241
- ISSN
0044-2313
- Publication type
Article
- DOI
10.1002/zaac.201200476