Layered mixed metal oxyhalide intergrowths, of the type Bi4MO8Cl (M = Ta, Nb, V) – Bi2LnO4Cl (Ln = Gd, La, Y), have recently been targeted as promising photocatalytic materials due to their anticipated unique crystal structures, photostability, and visible light absorption. Successful intergrowth formation for the Bi4TaO8Cl–Bi2GdO4Cl and Bi4NbO8Cl–Bi2GdO4Cl systems has been reported, but expanding to the other compositions has yet to be fully demonstrated. Here, the investigations into the synthesis of Bi4TaO8Cl–Bi2YO4Cl intergrowths are reported. A range of stoichiometric compositions were targeted via a flux salt method, and optimized by varying time, temperature, and identity of the flux salt used. Products were analyzed by Scanning Electron Microscopy coupled with Energy Dispersive X-Ray Spectroscopy (SEM-EDS), Powdered X-Ray Diffraction (PXRD), and Scanning Transmission Electron Microscopy (STEM) coupled with EDS. Successfully synthesized intergrowth materials would have uniform crystal morphology by SEM, be phase pure by PXRD, and show homogenous composition both at the bulk and nano scale. However, this was not observed experimentally. While the targeted compositions showed minimal impurities and homogenous crystal morphologies, STEM-EDS revealed extreme variation from one crystal to the next in terms of the atomic percentages of tantalum and yttrium. Nanoscale mixing of the appropriate elements was evident but crystals of different intergrowth stoichiometries existed within the same sample. These results occurred regardless of reaction conditions, breaking the trend seen thus far in the family of Bi4MO8Cl (M = Ta, Nb, V) – Bi2LnO4Cl (Ln = Gd, La, Y) materials. Therefore, a crystallographic study of the family of possible layered oxyhalide intergrowth materials was conducted, supported by experimental data, to obtain crystallographic trends that can be correlated to the feasibility of intergrowth formation. This analysis is anticipated to expand the library of potential photocatalytic materials for renewable energy and similar field applications.

Feasibility of Bi4MO8Cl– Bi2LnO4Cl (M=Ta, Nb, V; Ln=Y, La, Gd) intergrowth formation

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