Dynamic processes in the superionic conductor LaF3 at high temperatures as studied by spin-lattice relaxation dispersion

Abstract

By nuclear magnetic resonance spin-lattice relaxation dispersion in LaF3, measured in the frequency range from 60 kHz to 284 MHz, dynamic processes with correlation times in the range from 10-5 to 10-10 s are studied. This allows us to trace fluorine dynamics in the temperature range from 303 to 1400 K. Two motional modes, a fast one and a slow one, are identified. Both motional processes are found not to be of Bloembergen-Purcell-Pound type but obey a log-Gaussian distribution of correlation times, thus reflecting the potential energy landscape in the superionic state. Below 1000 K, the activation energy of fluorine diffusion is 0.36 eV for the fast ions, and 0.57 eV for the slow ones. At higher temperatures, the activation energies change drastically. Above 20 MHz, where most relaxation studies have been performed so far, an additional contribution to relaxation, which is probably induced by paramagnetic centres, is found to be dominant.

1H NMR study of hydrogen self-diffusion in ternary Ti–V–Cr alloys

“…The experiment was carried out using the home-made 1 SFG NMR relaxometer at 100 MHz in a static field gradient of 51.3 ± 0.3 T/m within the temperature range from 294 K to 433 K using a high temperature probe [20]. The temperature of the samples was controlled with the accuracy of 0.5 K.…”

Hydrogen diffusion in metal-hydrogen systems via NMR and DFT

“…Diffusion measurements were carried out using a homemade SFG relaxometer 2 [35] at 100 MHz in a static field gradient of 51.3 ± 0.3 T/m in the temperature range from 294 to 433 K using a high temperature probe [36]. The temperature of the samples was controlled with the accuracy of 0.5 K.…”

Активационные энергии движения ионов в наноразмерной решетке суперионного проводника LaF-=SUB=-3-=/SUB=-

“…Как известно, активное разупорядочение анионной подрешетки, например в кристалле LaF 3 , определяе-мое высокой подвижностью ионов фтора, наблюдается в области температур 260−540 K и продолжается до температуры плавления решетки [10][11][12]. Причем в области 260−320 K разупорядочение решетки опреде-ляется движением ионов в подрешетке F 1 , составля-ющих 2/3 от общего числа ионов фтора.…”

“…Оставшиеся ионы фтора, называемые F 2 и F 3 , образуют вместе с катионами металла анионно-катионные плоскости в структуре решетки. Подрешетки этих ионов разупорядо-чиваются ( " плавятся") при температурах, превышающих 360−420 K [12][13][14].…”