Semiconducting Sm3GaSe5O with trigonal bipyramidal GaSe5 units

The oxyselenide Sm3GaSe5O was prepared by reaction of Sm2O3, Sm, Ga2Se3, and Se at 950 degrees C. It adopts a new monoclinic structure type (space group P21/m, a = 11.042(9) angstrom, b = 3.9761(3) angstrom, c = 21.2458(17) angstrom, beta = 92.2436(14)degrees, Z = 4) built up of Sm-Se, Sm-O, and Ga-Se blocks. GaSe5 trigonal bipyramids, which are un-precedented, are the most unusual feature of this structure. Electronic structure calculations corroborate the occurrence of primarily ionic bonding within the Sm-Se and Sm-O blocks and covalent bonding within the Ga-Se blocks. Optical measurements reveal a nearly direct band gap of 1.2 eV, narrower than those of many other oxychalcogenides.

Automated summary

The oxyseleide Sm3GaSe5O, prepared through a reaction between Sm2O3, Sm, Ga2Se3, and Se at a high temperature, exhibits a newly discovered monoclinic crystal structure. The most remarkable feature of this structure is the presence of GaSe5 trigonal bipyramids, which have not been seen before. Optical measurements show that it has a narrower band gap compared to other oxychalcogenides.