Increased electrical conduction with high hole mobility in anti-ThCr2Si2-type La2O2Bi via oxygen intercalation adjacent to Bi square net

Abstract

Anti-ThCr2Si2-type RE2O2Bi (RE = rare earth) with a Bi square net is known to show an insulator–metal transition by substituting RE. In this study, La2O2Bi polycrystals with different oxygen nonstoichiometry were synthesized. As the amount of oxygen in La2O2Bi increased, the c-axis length was expanded due to the generation of an additional 4e site for excess oxygen, while the a-axis length remained almost constant, indicating the separation of Bi square nets by oxygen intercalation. Concomitantly, transformation of insulating La2O2Bi into metallic La2O2Bi occurred with the change in carrier polarity from the n- to p-type. Despite its polycrystalline form, La2O2Bi with the largest amount of oxygen showed a rather high hole mobility of 85 cm2 V−1 s−1 among other layered oxypnictides and oxychalcogenides.

Increased hole mobility in anti-ThCr2Si2-type La2O2Bi co-sintered with alkaline earth metal oxides for oxygen intercalation and hole carrier doping

“…La2O2Bi with xCa = 0.10, 0.20, and xSr = 0.03, 0.10 showed a lower resistivity at 2−300 K than those of La2O2.08Bi and La2O2.20Bi reported previously (Fig. 3a), 15 in addition to absence of resistivity upturn with decreasing temperature. This result suggests a larger amount of intercalated oxygen in La2O2Bi with xCa = 0.10, 0.20 and xSr = 0.03, 0.10 than that in La2O2.20Bi, as was exemplified in the longer c-axis length (Fig.…”

“…All AEO serves as an oxidant to intercalate oxygen into La2O2Bi resulting in the longer c-axis length (> 14.00 Å) than those of La2O2+δBi in previous study (Fig. 2a), 15 in which the excess oxygen was intercalated by controlling the nominal oxygen composition together with significant amounts of impurity phases (Fig. S4 † and Table S1 †).…”

“…The similar slope of the Hall resistivity for La2O2Bi with xCa = 0.10, 0.20, and xSr = 0.03 to those of La2O2.08Bi and La2O2.20Bi indicated their similar amounts of hole carrier density, representing that the excess oxygen was not effective carrier dopant, as was discussed in the previous study. 15 On the other hand, the smaller slope for La2O2Bi with xSr = 0.10 was caused by the increased hole carrier density due to Sr substitution with La, as was observed in other layered compounds such as La2−xSrxCuO4 and La1−xSrxNiAsO. 19,20 The resistivity and mobility at 10 K are summarized as a function of hole carrier density in Fig.…”

“…La (99.9%), La2O3, Bi (99.9%), CaO, SrO (98%), and BaO (99%) powders were mixed and pelletized under 10 MPa in a nitrogen-filled glovebox to form nominal compositions of (La1−xAEx)2O1.6Bi (0 ≤ xAE ≤ 0.20) (AE = Ca, Sr, Ba), which transformed into stoichiometric or oxygen intercalated (La1−xAEx)2O2Bi after sintering as reported previously. 15 The pellets covered with Ta foils were sintered in evacuated quartz tubes at 773 K for 7.5 hours and then at 1273 K for 10 hours. The sintered products were ground and pelletized under 20 MPa again in the glovebox, followed by the sintering in evacuated quartz tubes at 1273 K for 10 hours.…”

“…[12][13][14] Recently, insulating La2O2Bi with the longest a-axis length was transformed into a metallic one with high hole mobility of 85 cm 2 V −1 s −1 by expanding the c-axis length via oxygen intercalation. 15 In this study, La2O2Bi was co-sintered with alkaline earth metal oxides (CaO, SrO, and BaO). CaO and BaO served as oxygen intercalants, while SrO served as not only oxygen intercalant but also hole dopant via Sr substitution with La.…”