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Table 1 Positional and thermal parameters, selected interatomic distances and average Bi valence for SrBiO3 and Sr0.4K0.6BiO3
SrBiO3 Sr0.4K0.6BiO3...................................................................................................................................................................................................................................................................................................................................................................Space group P21/n I4/mcm
Lattice parameters a 5:94802, b 6:09512, c 8:48543, [H9252] 90:0636[H11034] a 5:94162, c 8:43944
Sr(K) x, y, z 0.0152(7), 0.5455(4), 0.251(1) 0, 0.5, 0.75 U (A2) 0.0078(7) 0.016(1)
Bi1 x, y, z 0, 0, 0 0, 0, 0 U (A2) 0.0045(6) 0.0017(5)
Bi2 x, y, z 0, 0, 0.5 U (A2) 0.0045(6)
O1 x, y, z 0.4056(7), 0.4617(7), 0.241(1) 0, 0, 0.25 U (A2) 0.019(1) U11, U33: 0.033(3), 0.009(2)
O2 x, y, z 0.284(1), 0.190(1), 0.546(1) 0.2219(5), 0.7219(5), 0 U (A2) 0.019(2) U11, U33: 0.011(1), 0.060(3)
O3 y, y, z 0.187(1), 0.714(1), 0.556(1) U (A2) 0.012(2)
Rw, x2 7.11%,1.60 8.19%,1.88 Sr(K)O (A) 3.484(6), 2.556(6), 3.618(5) 2.620(5), 3.76(1), 3.01(1), 2.85(1), 2.55(1), 3.03(1), 3.83(1), 2.50(1), 2.83(1) 2:97082 [H11003] 4, 2:8142 [H11003] 4, 3:1502 [H11003] 4 Bi1O (A) 2:281 [H11003] 2, 2:3177 [H11003] 2, 2:3216 [H11003] 2 2:10984 [H11003] 2, 2:1143 [H11003] 4 Bi2O (A) 2:141 [H11003] 2, 2:0887 [H11003] 2, 2:1237 [H11003] 2 v(Bi1) 3.21 4.62 v(Bi2) 4.57 ...................................................................................................................................................................................................................................................................................................................................................................U, mean square temperature displacement; R , weighted prole agreement factor; v, valence.
distinct distorted octahedral sites. The positional and thermal parameters after the last cycle of renement, as well as the BiO and SrO interatomic distances, are given in Table 1. Attempts to rene the cationic or anionic site occupancies did not lead to any deviation from full occupancies. The average BiO distances are2.30(1) and 2.12(1) for the two sites. The average valences of Bi1 and Bi2 calculated with the Zachariasen formula10 and the constants reported previously11 are +3.21 and +4.57, respectively. As with BaBiO39,11, this indicates a partial disporportionation of the Bi cations into Bi3+ and Bi5+, which occupy the two distinct crystal-lographic Bi1 and Bi2 sites. This charge localization is in agreement with the insulating properties of this compound.
The structure of Sr0.4K0.6BiO3 has been rened in the I4/mcm
space group (as with BaPb1xBixO3 in the superconducting region). The main results are reported in Table 1 and a structural model is shown in Fig. 3. The rened K content is 0.56(2), in good agreement with the EDS data. The temperature factors of the oxygen atoms are highly anisotropic with anomalously large...