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Abstract

-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 -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, -KCrO2, crystallizes in the -RbScO2 type of structure [P63/mmc; a = 3.0427(4) angstrom, c = 11.924(2) angstrom; 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 -KCrO2, and clearly identified in the specific heat measurements, a -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 (eff) of the order of 3.91 B, corresponding to a g-factor [eff /B = g[S(S+1)]1/2] of 2.019 well in accordance for Cr3+ (d3 system) with spin S = 3/2.