Bi³⁺/M²⁺ Oxyphosphate: A Continuous Series of Polycationic Species from the 1D Single Chain to the 2D Planes. Part 2: Crystal Structure of Three Original Structural Types Showing a Combination of New Ribbonlike Polycations

With the assistance of structural models deduced from the high-resolution electron microscope (HREM) investigation presented in Part 1 of this work, three new structural types were pointed out in Bi2O3−MO−P2O5 ternary systems. Their crystal structures are built on the arrangement of 2D polycationic ribbons formed of edge-sharing O(Bi,M)4 tetrahedra and isolated by PO4 groups. Prior to this study, materials with ribbons up to n = 3 tetrahedra wide have been discovered. The original structures presented here display longer n = 4−6 cases, which suggests a possible continuous series of polycationic entities that range from the single chain (one tetrahedron wide) to the infinite [Bi2O2]2+ Aurivillius layer. The ribbons with n > 3 show strong structural modifications that are able to bring a good ribbon−phosphate cohesion. In addition to these fascinating structural results, this work fully confirms the validity of the decoding established from HREM images of a single crystallite in inhomogeneous mixtures.借助本研究第一部分中报道的高分辨电子显微镜（high-resolution electron microscope, HREM）研究所推导得到的结构模型，我们在Bi₂O₃−MO−P₂O₅三元体系中发现了三种全新的结构类型。其晶体结构以共享边的O(Bi,M)₄四面体构成的二维多阳离子带（2D polycationic ribbons）为排布基础，并被PO₄基团相互分隔。在本研究开展前，已发现的此类多阳离子带的宽度最多包含n=3个四面体单元。本次报道的原创结构则展示了n=4~6的更宽带型，这暗示存在一条连续的多阳离子实体演化序列：从单链（宽度为1个四面体）直至无限延伸的[Bi₂O₂]²+奥里维留斯（Aurivillius）层。当n>3时，多阳离子带会发生显著的结构修饰，从而实现带与磷酸盐基团之间的良好结合。除上述极具科学价值的结构研究成果外，本研究还充分验证了从非均匀混合物中单微晶的高分辨电子显微镜图像所建立的结构解析方法的有效性。