https://nova.newcastle.edu.au/vital/access/ /manager/Index en-au 5 https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:53732 Wed 10 Jan 2024 11:31:02 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:43114 Tue 13 Sep 2022 14:04:23 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:43310 Thu 15 Sep 2022 14:01:32 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:27940 ISOTROPY. For HTB, there is one obvious tilting pattern, leading to a structure in space group P6₃/mmc. This differs from the space group P6₃/mcm frequently quoted from X-ray studies - these studies have in effect detected only displacements of the W cations from the centres of the WO₆ octahedra. The correct space group, taking account of both W ion displacement and the octahedral tilting, is P6₃22 - structures in this space group and matching this description have been reported. A second acceptable tilting pattern has been found, leading to a structure in P6/mmm but on a larger '2 x 2 x 2' unit cell - however, no observations of this structure have been reported. For TTB, a search at the special points of the Brillouin zones revealed only one comparable tilting pattern, in a structure with space-group symmetry I4/m on a '2^1/2 x 2^1/2 by 2' unit cell. Given several literature reports of larger unit cells for TTB, we conducted a limited search along the lines of symmetry and found structures with acceptable tilt patterns in Bbmm on a '2^1/22 x 2^1/2 x 2' unit cell. A non-centrosymmetric version has been reported in niobates, in Bbm2 on the same unit cell.]]> Sat 24 Mar 2018 07:36:10 AEDT ]]>