Different crystal chemistries of the117Cd→117

Abstract

The nuclear-electric-quadrupole interactions at 117 In and 111 Cd nuclei arising from 117 Cd and 111m Cd, respectively, each chemically introduced in ferroelectric LiNbO 3 (T C ϭ1483 K) and LiTaO 3 (T C ϭ938 K) polycrystals, were studied by measuring the time-differential perturbed angular correlation of ␥ rays over a temperature range from 4.2 to 1243 K. Well-defined, essentially single, static electric quadrupole frequencies were observed for 117 In and 111 Cd in the oxides. It has been established that both In and Cd occupy the Li sites of LiNbO 3 and LiTaO 3 . In the case of LiTaO 3 , the temperature dependences of the quadrupole frequencies Q of 117 In and 111 Cd clearly change at around T C ϭ938 K, reflecting the ferroelectric-to-paraelectric phase transition. In both oxides, it might be expected that the temperature dependence of Q of 117In would agree with that of 111 Cd. However, it is so only at low temperatures, including room temperature. There is a significant difference at high temperatures: Q of 117 In is strongly dependent on temperature, whereas Q of 111 Cd is weakly dependent. It is considered that the Cd ions at the Li sites are in peculiar physicochemical states.

Mechanism of the ferroelectric phase transitions inLiNbO3andLiTaO3Ohkubo1, Murakami2, Saito3 et al. 2002Phys. Rev. B121170View full textAdd to dashboardCite

“…We performed PAC measurements on 117 In ͑arising from 117 Cd via nuclear decay͒ in polycrystalline samples of 8-mol % In-doped LT in a temperature range covering T C of 818 K. In addition, we performed PAC measurements on 111 Cd (← 111m Cd). Although Cd also occupies the Li site, as was confirmed in our previous PAC measurements for LN and LT, 7 the order-disorder transition of Cd can be different from that of In. Owing to the much larger ionic size 8 of Cd 2ϩ ͑95 pm͒ than that of Li ϩ and In 3ϩ , Cd may not even be dynamically disordered.…”

Behavior of Impurities In and Cd in the LiNbO<SUB>3</SUB>-LiTaO<SUB>3</SUB> System

“…In a previous work, 11) we confirmed that an order of 1 mol% of Cd occupy the Li sites of LiNbO 3 and LiTaO 3 . We now examine whether an order of 10 mol% of Cd occupy the Li sites and thus a compound with the chemical formula Li 0.833 Cd 0.083 TaO 3 was actually prepared.…”

“…9)) can be explained as follows. Since the charge on an In ion at the Li site of LiTaO 3 is considered to be close to 3+, 11) and its ionic size (80 pm) is about the same as that of Li + (76 pm), 4) the In ion must come closer to the upper oxygen triangle than does a Li ion, because of its stronger Coulomb interaction with oxygen ions. This makes the inner space of the triangle more open, and thus a single In ion doped in LiTaO 3 as an impurity becomes disordered at a much lower temperature than Li would require.…”

“…Additional measurements of ω Q of 111 Cd in the oxides, 11,12) which also occupy those Li sites, 11) showed their temperature dependences to be quite different from those of 117 In. In the case of Li 0.8 In 0.067 TaO 3 , the temperature dependence does not even reflect the phase transition at T C = 818 K. This observation indicates that, different from In, Cd is not disordered in the paraelectric phase.…”

Measurement of electric field gradient at 117In on the Cu-site in mavicyanin by perturbed angular correlation of γ-rays

“…The PAC measurement system used in this study is the same that was mentioned in [9]. The directional anisotropy A 22 G 22 (t) derived from the measurement, denoted as R(t) in Figure 2, is expressed as follows for an ensemble of randomly oriented molecules in liquid but in inactive molecular motion.…”