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RESEARCH PRODUCT

Crystal structure, dielectric properties and molecular motions in ( i -C 4 H 9 NH 3 ) 3 Bi 2 Br 9

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Abstract The crystal structure of ( i -C 4 H 9 NH 3 ) 3 Bi 2 Br 9 at room temperature has been determined and refined to R =0.036. The crystal is orthorhombic, space group Ama 2. The structure is built up of the i -butylammonium cations and isolated Bi 2 Br 9 3− anions. The complex dielectric permittivity along the a -axis has been measured between 500 Hz and 1000 MHz in the vicinity of two phase transitions at 252 and 263 K. The dielectric response close to 252 K is well described by the Debye equation. The activation energy of the reorientation of the i -butylammonium cations is found to be 0.68 eV. The temperature dependencies of the proton relaxation time T 1 and of the second moment of 1 H NMR has been studied between 120 and 390 K. The relaxation time T 1 reveals one minimum due to the motion of both NH 3 and CH 3 groups. Analysis of the relaxation data yields the activation energy barriers for the NH 3 and CH 3 groups motion of 0.113 and 0.037 eV, respectively. The NMR studies suggest that the 263 K phase transition is connected with the reorientation of the cations as a whole.