title: Selective synthesis of monazite- and zircon-type LaVO(4) nanocrystals.
abstract: Pure monoclinic (m-) and tetragonal phased (t-) LaVO(4) nanocrystals could be obtained by a hydrothermal method in a controllable way with additives. It is found that chelating ligands, such as ethylenediaminetetraacetic acid [EDTA or H(4)L, where L(4-) = (CH(2)COO)(2)N(CH(2))(2)N(CH(2)COO)(2)(4-)], favor the formation of t-LaVO(4) and can induce the polymorph transformation from stable m-LaVO(4) to metastable t-LaVO(4). Further studies demonstrated the important roles of chelating ligands in this transformation process. Careful investigation over the phase transition from t- to m-LaVO(4) was also conducted with high-temperature X-ray diffraction (HTXRD) studies. The phase transition occurred at 850 degrees C, which is about 250 degrees C higher than for the bulk. The enhanced thermal stability of the nanosized metastable t-LaVO(4) may come from the small size effect. Our capability of obtaining and stabilizing t-LaVO(4) not only benefits the wider applications based on LaVO(4) due to the improved luminescent and catalytic performance but also provides a new idea in the studies of polymorph control and selective synthesis of inorganic materials.
authors.affiliation: State Key Lab of Rare Earth Materials Chemistry and Applications and PKU-HKU Joint Lab in Rare Earth Materials and Bioinorganic Chemistry, Peking University, Beijing 100871, China.
authors.forename: Chun-Jiang
authors.initials: CJ
authors.lastname: Jia
authors.forename: Ling-Dong
authors.initials: LD
authors.lastname: Sun
authors.forename: Li-Ping
authors.initials: LP
authors.lastname: You
authors.forename: Xiao-Cheng
authors.initials: XC
authors.lastname: Jiang
authors.forename: Feng
authors.initials: F
authors.lastname: Luo
authors.forename: Yu-Cheng
authors.initials: YC
authors.lastname: Pang
authors.forename: Chun-Hua
authors.initials: CH
authors.lastname: Yan