Preparation and HREM Characterization of a Protonated Form of a Layered Perovskite Tantalate from an Aurivillius Phase Bi_2SrTa_2O_9 via Acid Treatment

摘要

An Aurivillius phase, Bi_2SrTa_2O_9, which consists of perovskite-like slabs and bismuth oxide sheets, was treated with 3 M hydrochloric acid for 72 h, and the resultant product was characterized. Scanning electron microscopy investigation indicated that no morphological chamge occurred during the acid treatment. X-ray difraction (XRD) analysis revealed that the product exhibited tetragonal symmetry with a = 0.391 +- 0.004 nm and c = 0.98 +- 0.01 nm, and the a parameter is consistent with a typical value for cubic perovskite oxides. High-resoution electron microscopy (HREM) observations along both [001] and [010] showed that the structure of the perovskite-like slabs in Bi_2SrTa_2O_9 was retained after the acid treatment. The compositional analyses revealed the loss of a large portion of bismuth and a part of strontium (present in the bismuth oxide sheets due to B<-> Sr disorder) and the introduction of protons. These observations indicate that the bismuth oxide sheets in Bi_2SrTa_2O_9 were selectively leached and that protons were introduced into the interlayer space to form a protonated layered perovskite, H_(1.8)[Sr_(0.8)Bi_(0.2)Ta_2O_7] consisted of perovskite-like slabs stacked without displacement, HREM observation along [010] demonstrated that both a simple stacking sequence without displacement (P-type) and a stacking sequence with a relative dislacement by (a + b)/2 (I-type) were present in H_(1.8)[Sr_(0.8)Bi_(0.2)Ta_2O_7].