α-LiMB9O15 (M = Sr, Pb): flexible [B3O7] units leading to the low temperature phase of β-LiMB9O15 (M = Sr, Pb)

Under the regulation of a metal cation with a large radius, borates formed from [B 3 O 7 ] groups have high structural flexibility, and the low-temperature phases of α-LiSrB 9 O 15 and α-LiPbB 9 O 15 were obtained.