10.1021/cm049234y.s007 Eun Ok Chi Eun Ok Chi Alberto Gandini Alberto Gandini Kang Min Ok Kang Min Ok Lei Zhang Lei Zhang P. Shiv Halasyamani P. Shiv Halasyamani Syntheses, Structures, Second-Harmonic Generating, and Ferroelectric Properties of Tungsten Bronzes:  A<sub>6</sub>M<sub>2</sub>M‘<sub>8</sub>O<sub>30</sub> (A = Sr<sup>2+</sup>, Ba<sup>2+</sup>, or Pb<sup>2+</sup>; M = Ti<sup>4+</sup>, Zr<sup>4+</sup>, or Hf<sup>4+</sup>; M‘ = Nb<sup>5+</sup> or Ta<sup>5+</sup>) American Chemical Society 2004 Ba 6 Hf 2 Nb 8 O 30 hysteresis loops polarization vs Ba 6 Zr 2 Ta 8 O 30 material Cm 2 m Ferroelectric Properties Ba 6 Ti 2 Nb 8 O 30 SHG efficiency Spontaneous polarization values noncentrosymmetric space groups Ba 6 Ti 2 Ta 8 O 30 Pb 6 Ti 2 Nb 8 O 30 Ba 6 Hf 2 Ta 8 O 30 P 4 bm 1064 nm radiation Sr 6 Ti 2 Nb 8 O 30 Ba 6 Zr 2 Nb 8 O 30 532 nm SHG efficiencies range tungsten bronze oxides Pba 2 Sr 6 Ti 2 Ta 8 O 30 compounds exhibit 2004-09-21 00:00:00 Figure https://acs.figshare.com/articles/figure/Syntheses_Structures_Second_Harmonic_Generating_and_Ferroelectric_Properties_of_Tungsten_Bronzes_A_sub_6_sub_M_sub_2_sub_M_sub_8_sub_O_sub_30_sub_A_Sr_sup_2_sup_Ba_sup_2_sup_or_Pb_sup_2_sup_M_Ti_sup_4_sup_Zr_sup_4_sup_or_Hf_sup_4_sup_M_Nb_sup_5_sup_or_Ta_/3324358 Nine tungsten bronze oxides, A<sub>6</sub>M<sub>2</sub>M‘<sub>8</sub>O<sub>30</sub> (A = Sr<sup>2+</sup>, Ba<sup>2+</sup>, or Pb<sup>2+</sup>; M = Ti<sup>4+</sup>, Zr<sup>4+</sup>, or Hf<sup>4+</sup>; M‘ = Nb<sup>5+</sup> or Ta<sup>5+</sup>), have been synthesized and characterized. Although structurally very similar, the nine materials are not isostructural. The materials crystallize in noncentrosymmetric space groups, <i>P</i>4<i>bm</i> (no. 100) for Ba<sub>6</sub>Ti<sub>2</sub>Nb<sub>8</sub>O<sub>30</sub>, Ba<sub>6</sub>Ti<sub>2</sub>Ta<sub>8</sub>O<sub>30</sub>, Ba<sub>6</sub>Zr<sub>2</sub>Nb<sub>8</sub>O<sub>30</sub>, Ba<sub>6</sub>Zr<sub>2</sub>Ta<sub>8</sub>O<sub>30</sub>, Ba<sub>6</sub>Hf<sub>2</sub>Nb<sub>8</sub>O<sub>30</sub>, and Ba<sub>6</sub>Hf<sub>2</sub>Ta<sub>8</sub>O<sub>30</sub>; <i>Pba</i>2 (no. 52) for Sr<sub>6</sub>Ti<sub>2</sub>Nb<sub>8</sub>O<sub>30</sub> and Sr<sub>6</sub>Ti<sub>2</sub>Ta<sub>8</sub>O<sub>30</sub>; and <i>Cm</i>2<i>m</i> (no. 38) for Pb<sub>6</sub>Ti<sub>2</sub>Nb<sub>8</sub>O<sub>30</sub>. All of the compounds exhibit second-order nonlinear optical behavior, i.e., second-harmonic generation (SHG), by frequency doubling 1064 nm radiation to 532 nm. The SHG efficiencies range from 10 to 600 × SiO<sub>2</sub>. The reported materials are also ferroelectric, as demonstrated by hysteresis loops (polarization vs electric field). Spontaneous polarization values (<i>P</i><sub>s</sub>) range from 0.79 to 12.1 μC/cm<sup>2</sup>. The magnitude of the SHG efficiency and ferroelectric polarization are strongly dependent on the A, M, and M‘ cations.