Crystal Chemistry, X-ray Diffraction Reference Patterns, and Band Gap Studies for (BaxSr1-x)2CoWO6 (x=0.1, 0.2, 0.3, 0.5, 0.7, 0.9)
Winnie K. Wong-Ng, Guangyao Liu, Yuqi Yang, Rola M. Derbeshi, Donald A. Windover, James A. Kaduk
X-ray reference powder patterns and structures have been determined for a series of cobalt- and tungsten-containing cubic alkaline-earth perovskites, (BaxSr1-x)2CoWO6 (x=0.1, 0.2, 0.3, 0.5, 0.7, 0.9). The structure of the end members of the series, Sr2CoWO6 and Ba2CoWO6, were tetragonal and cubic respectively, agreeing with the literature data. From Rietveld refinements, it was found that when x=0.1 and 0.2, the structure was tetragonal I4/m (a= 5.60481(6) Å and 5.62305(11) Å, and c= 7.97989(12) Å, and 7.9847(2) Å, respectively; Z=2). When x > 0.2, the structure was cubic (Fm3m, No 225; Z=4) (from x=0.3 to 0.9, a increases from 7.98399(13) Å to 8.08871(10) Å). This series of compounds exhibit the characteristics of distorted double perovskite structure, with the rotational mismatch angles of 25° and 16° for x=0.1 to 0.2 compounds (tetragonal case). The bond valence sum (BVS) values for the alkaline-earth (Ba,Sr) sites in all (BaxSr1-x)2CoWO6 members are greater than the ideal value of 2.0, indicating over-bonding situation, whereas for the W sites, as x increases, a change from under-bonding to slightly over-bonding situation was observed. DFT calculations revealed that while Sr2WCoO6 is a semiconductor, Ba2WCoO6 and SrBaWCoO6 are half-metals. Powder X-ray diffraction patterns of this series of compounds (BaxSr1- x)2CoWO6, with x=0.1, 0.2, 0.3, 0.5, 0.7 and 0.9, have been submitted to be included in the Powder Diffraction File (PDF).