“…Two commercially available powders, amorphous boron (aB, 97%; Wako Pure Chemical Industries, Ltd., Osaka, Japan) and B 2 O 3 powder (99.0%; Kanto Chemical Co., Inc., Tokyo, Japan), were used as the starting materials. The mixing procedure for the B 2 O 3 and aB raw powders was the same as that in our previous works . The raw powders were mixed in 6:1 and 10:1 aB:B 2 O 3 mole ratios (B 6 O‐6:1 and B 6 O‐10:1 ceramics, respectively).…”