On structural phase transitions in piperidinium halogenoantimonates(III) and bismuthates(III): X-ray, calorimetric, dilatometric, dielectric and Raman studies

✍ Scribed by B. Bednarska-Bolek; J. Zaleski; G. Bator; R. Jakubas

• Publisher: Elsevier Science
• Year: 2000
• Tongue: English
• Weight: 466 KB
• Volume: 61
• Category: Article
• ISSN: 0022-3697
• DOI: 10.1016/s0022-3697(99)00414-x

✦ Synopsis

Three piperidinium analogues: (C 5 H 10 NH 2 ) 2 BiCl 5 , (C 5 H 10 NH 2 ) 2 BiBr 5 and (C 5 H 10 NH 2 ) 2 SbBr 5 have been studied by means of differential scanning calorimetry, thermal expansion, dielectric and Raman scattering techniques. Each piperidinium salt undergoes one high-temperature structural phase transition, which has been classified as an "order-disorder" type. All transitions are connected with onset of reorientational motion of the organic cations. The X-ray studies on (C 5 H 10 NH 2 ) 2 BiCl 5 show that it crystallises in orthorhombic Pna2 1 space group. The structure has been refined to R 0:0336: It consists of onedimensional BiCl 2Ϫ

5 n polyanionic chains and two non-equivalent piperidinium cations, one ordered and one disordered. The disorder is realised by splitting all atoms between two positions with half occupancy. The Raman studies of the polycrystalline (C 5 H 10 NH 2 ) 2 BiCl 5 performed in the frequency region between 3500 and 50 cm Ϫ1 show that the vibrational state of the piperidinium cation changes around the phase transition point.