title: Role of acentric displacements on the crystal structure and second-harmonic generating properties of RbPbCO3F and CsPbCO3F.
abstract: Two lead fluorocarbonates, RbPbCO3F and CsPbCO3F, were synthesized and characterized. The materials were synthesized through solvothermal and conventional solid-state techniques. RbPbCO3F and CsPbCO3F were structurally characterized by single-crystal X-ray diffraction and exhibit three-dimensional (3D) crystal structures consisting of corner-shared PbO6F2 polyhedra. For RbPbCO3F, infrared and ultraviolet-visible spectroscopy and thermogravimetric and differential thermal analysis measurements were performed. RbPbCO3F is a new noncentrosymmetric material and crystallizes in the achiral and nonpolar space group P6m2 (crystal class 6m2). Powder second-harmonic generation (SHG) measurements on RbPbCO3F and CsPbCO3F using 1064 nm radiation revealed an SHG efficiency of approximately 250 and 300 × α-SiO2, respectively. Charge constants d33 of approximately 72 and 94 pm/V were obtained for RbPbCO3F and CsPbCO3F, respectively, through converse piezoelectric measurements. Electronic structure calculations indicate that the nonlinear optical response originates from the distorted PbO6F2 polyhedra, because of the even-odd parity mixing of the O 2p states with the nearly spherically symmetric 6s electrons of Pb(2+). The degree of inversion symmetry breaking is quantified using a mode-polarization vector analysis and is correlated with cation size mismatch, from which it is possible to deduce the acentric properties of 3D alkali-metal fluorocarbonates.
authors.affiliation: Department of Chemistry, University of Houston , 112 Fleming Building, Houston, Texas 77204-5003, United States.
authors.forename: T Thao
authors.initials: TT
authors.lastname: Tran
authors.forename: P Shiv
authors.initials: PS
authors.lastname: Halasyamani
authors.forename: James M
authors.initials: JM
authors.lastname: Rondinelli
mesh_terms: D002254:Carbonates / Q000737:chemistry*; D002586:Cesium / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004055:Differential Thermal Analysis; D005459:Fluorides / Q000737:chemistry*; D007854:Lead / Q000737:chemistry*; D008958:Models, Molecular; D012413:Rubidium / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D017550:Spectroscopy, Fourier Transform Infrared; D013818:Thermogravimetry
chemical_list: D002254:Carbonates; D002586:Cesium; D007854:Lead; D012413:Rubidium; D005459:Fluorides