New Fluoride Carbonates:
Centrosymmetric KPb<sub>2</sub>(CO<sub>3</sub>)<sub>2</sub>F and Noncentrosymmetric
K<sub>2.70</sub>Pb<sub>5.15</sub>(CO<sub>3</sub>)<sub>5</sub>F<sub>3</sub>
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Abstract
Two new potassium lead fluoride carbonates, KPb<sub>2</sub>(CO<sub>3</sub>)<sub>2</sub>F and K<sub>2.70</sub>Pb<sub>5.15</sub>(CO<sub>3</sub>)<sub>5</sub>F<sub>3</sub>, have been synthesized
and characterized. The materials were synthesized through solvothermal
and conventional solid-state techniques. KPb<sub>2</sub>(CO<sub>3</sub>)<sub>2</sub>F and K<sub>2.70</sub>Pb<sub>5.15</sub>(CO<sub>3</sub>)<sub>5</sub>F<sub>3</sub> were structurally characterized by single
crystal X-ray diffraction and exhibit two-dimensional crystal structures
consisting of corner-shared PbO<sub>6</sub>F and PbO<sub>6</sub>F<sub>2</sub> polyhedra. K<sub>2.70</sub>Pb<sub>5.15</sub>(CO<sub>3</sub>)<sub>5</sub>F<sub>3</sub> is noncentrosymmetric, and crystallizes
in the <i>achiral</i> and <i>nonpolar</i> space
group <i>P</i>6̅<i>m</i>2 (crystal class
−6m2). Powder second-harmonic generation (SHG) measurements
using 1064 nm radiation revealed a SHG efficiency of approximately
40 × α-SiO<sub>2</sub>, whereas a charge constant, <i>d</i><sub>33</sub>, of approximately 20 pm/V was obtained through
converse piezoelectric measurements. For the reported materials, infrared,
UV–vis, thermogravimetric, and differential thermal analysis
measurements were performed
