TY - JOUR
T1 - Crystal structure, magnetism and phase transformation in perovskites A2CrNbO6 (A = Ca, Sr, Ba)
AU - Choy, Jin Ho
AU - Hong, Seung Tae
AU - Choi, Kyoung Shin
PY - 1996/3/21
Y1 - 1996/3/21
N2 - According to the Rietveld refinement, Ca2CrNbO6 and Sr2CrNbO6 have been found to be monoclinic with a = 5.4195 (1) Å, b = 5.4907 (1) Å, c = 7.7073 (2) Å, and cubic with a = 7.8732 (1) Å(Fm3m, No. 225), respectively. Under atmospheric pressure, Ba2CrNbO6 crystallizes into an 8H hexagonal structure with a = 5.7404 (1) Å and c = 18.7744 (5) Å (P63/mmc, No. 196), but at high pressure (80 kbar) and high temperature (930°C), it undergoes a structural phase transformation to the cubic perovskite with a = 8.0550 (4) Å (Fm3m). Magnetic susceptibility measurements show that Ca2CrNbO6, Sr2CrNbO6 and Ba2CrNbO6 with cubic symmetry follow the Curie-Weiss law, while the magnetic behaviour of Ba2CrNbO6 with hexagonal symmetry is significantly different from the others. Magnetic calculations based upon several models indicate the presence of strong (Cr-Cr) covalent bonding through face sharing of the octahedra in the hexagonal phase. The variation of crystal structures and magnetic properties in these compounds can be rationalized in terms of cationic size and the nature of the covalent bonding between metal and oxygen ions.
AB - According to the Rietveld refinement, Ca2CrNbO6 and Sr2CrNbO6 have been found to be monoclinic with a = 5.4195 (1) Å, b = 5.4907 (1) Å, c = 7.7073 (2) Å, and cubic with a = 7.8732 (1) Å(Fm3m, No. 225), respectively. Under atmospheric pressure, Ba2CrNbO6 crystallizes into an 8H hexagonal structure with a = 5.7404 (1) Å and c = 18.7744 (5) Å (P63/mmc, No. 196), but at high pressure (80 kbar) and high temperature (930°C), it undergoes a structural phase transformation to the cubic perovskite with a = 8.0550 (4) Å (Fm3m). Magnetic susceptibility measurements show that Ca2CrNbO6, Sr2CrNbO6 and Ba2CrNbO6 with cubic symmetry follow the Curie-Weiss law, while the magnetic behaviour of Ba2CrNbO6 with hexagonal symmetry is significantly different from the others. Magnetic calculations based upon several models indicate the presence of strong (Cr-Cr) covalent bonding through face sharing of the octahedra in the hexagonal phase. The variation of crystal structures and magnetic properties in these compounds can be rationalized in terms of cationic size and the nature of the covalent bonding between metal and oxygen ions.
UR - http://www.scopus.com/inward/record.url?scp=33749025309&partnerID=8YFLogxK
U2 - 10.1039/ft9969201051
DO - 10.1039/ft9969201051
M3 - Article
AN - SCOPUS:33749025309
SN - 0956-5000
VL - 92
SP - 1051
EP - 1059
JO - Journal of the Chemical Society, Faraday Transactions
JF - Journal of the Chemical Society, Faraday Transactions
IS - 6
ER -