Temperature-dependent Raman scattering study on Cs4W11O35 and Rb4W11O35 systems

Dynamic electrophysical characterization of rubidium polytungstate, Rb4W11O35, under fast humidity impact

“…Rubidium polytungstate, Rb 4 W 11 O 35 , (RWO) belongs to oxides of the crystal structures related to the hexagonal tungsten bronze (K x WO 3 ) type [1], As distinct from simple and double tungstates (e. g. PbWO 4 , Bi 2 WO 6 , CsTaWO 6 ), which were proposed for scintillation devices [2,3], RWO is considered as promising one to be applied in nonlinear optics using second harmonic generation [4,5], and as a precursor for nanosheets with highly efficient photochromic effects in functional optics [6]. For some of binary tungstates, antiferroelectric [7] as well as ferroelastic and ferroelectric [4,5,8] properties are previewed.…”

“…For some of binary tungstates, antiferroelectric [7] as well as ferroelastic and ferroelectric [4,5,8] properties are previewed. The Raman scattering studies of RWO reveal phase transitions at 210 K and 100 K and none of them above room temperature [4,5].…”

Resolving old problems with layered polytungstates related to hexagonal tungsten bronze: phase formation, structures, crystal chemistry and some properties

“…62,63 The unit cell parameters close to the data 4,16,62 and our results (see 47,49 According to the symmetry/structure criteria, 87,88 the HTBlike polytungstates could also possess ferroelectric/ferroelastic properties due to their polar average structures with the above mentioned non-polar monoclinic or orthorhombic prototypes ( paraphases) within the atomic displacements smaller than 0.78 Å, while the largest atomic shifts in ferroelectrics and ferroelastics are about 1 and 1.25 Å, respectively. 88 Indeed, the ferroelectricity of K 2 W 7 O 22 47 and displacive phase transitions found for A 4 W 11 O 35 (A = Rb, Cs) 71,89 make us to expect similar properties for other HTB-like polytungstates. The presence of cationic vacancies, wide tunnels and interlayer space in the discussed structures can contribute to noticeable ionic conductivity, which has already been reported for HTB-type A x WO 3 (A = K, Rb, Cs).…”

“…This can be a convenient tool for designing layered oxides with a variable width of the HTB-like slabs, which then can be used for creating new oxide nanosheet materials. The structural features of these compounds (open and easily deformed structures with wide channels) can favor displacive phase transitions, dielectric anomalies, piezoelectric, nonlinear optical and ferroelectric properties, which have already been found for K 2 W 7 O 22 47 and A 4 W 11 O 35 (A = Rb, Cs) 71,89 and are typical of many complex oxides related to HTB. [73][74][75]79,96 These data and the results of our structural studies and SHG measurements of the layered HTB-like polytungstates indicate that they can be promising nonlinear optical, ferroelectric, and ferroelastic materials.…”

“…The doubling seems to be caused by both out-of-center displacements of the W atoms in their oxygen octahedra due to the second-order Jahn-Teller (SOJT) effect for the d 0 cations 68 and tilting the cornersharing octahedra along the doubled axis, which are often observed in HTB and related tungsten oxides. 69,70 Obviously, these effects lead to disordering of the tungsten and oxygen atoms in our average structural models of the HTB-like polytungstates and diffuse scattering in their crystals, which may indicate displacive or order-disorder phase transitions observed in A 4 W 11 O 35 (A = Rb, Cs) 71 and many HTB-related tungsten oxides. [72][73][74][75] Discrepancies in the lattice dimensions and symmetry of the HTB-like polytungstates (Table 4) can also be caused by forming various superstructures (including metastable ones) at such phase transitions.…”