title: New ferroelectrics based on divalent metal ion alum.
abstract: A detailed study of two alum-type complexes containing the SeO(4)(2-) anion, 1,4-diazoniabicyclo[2.2.2]octane hexaaquacopper(II) bis(selenate) [(H(2)dbco)Cu(H(2)O)(6)(SeO(4))(2), 1] and its deuterated analogue (D(2)dbco)Cu(D(2)O)(6)(SeO(4))(2) (2), has revealed that 1 and 2 are new ferroelectrics that undergo a paraelectric-ferroelectric phase transition at ca. -140 to -138 degrees C as a result of order-disorder features of the cation ([H(2)dbco](2+) or [D(2)dbco](2+)) and anion (selenate). These are the first examples of ferroelectrics based on divalent metal anion alum analogues since the discovery of ferroelectrics based on trivalent metal anion alum in approximately 1960.
authors.affiliation: Ordered Matter Science Research Center, Southeast University, Nanjing 211189, PR China.
authors.forename: Wen
authors.initials: W
authors.lastname: Zhang
authors.forename: Li-Zhuang
authors.initials: LZ
authors.lastname: Chen
authors.forename: Ren-Gen
authors.initials: RG
authors.lastname: Xiong
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Nakamura
authors.forename: Songping D
authors.initials: SD
authors.lastname: Huang