Structural environment of chloride ion‐conducting solids based on lanthanum oxychloride

Abstract

The effect of the structural environment on the Cl− ion conductivity was demonstrated in LaOCl‐based solid electrolytes. By replacing the La3+ site with lower‐valent Mg2+ or Ca2+ ions, the conductivity was enhanced owing to the formation of a Cl− ion vacancy. Despite the same dopant content, the conductivity of La0.8Ca0.2OCl0.8 was considerably greater than La0.8Mg0.2OCl0.8. This enhancement of the conductivity was influenced by the high ionicity of the Cl− ions, which facilitated the weakening of the La‐Cl bond cleavage to conduct inside the lattice. The elongation of the La‐La distance, associated with the Cl− ion conduction, could also cause an increase of the conductivity.

Halide Replacement with Complete Preservation of Crystal Lattice in Mixed‐Anion Lanthanide Oxyhalides

“…In the LaOI structure,aprobable pathway for halide-ion diffusion is along the ab plane [32] along the halide slab that separates infinite fluorite-type blocks of (LaO) n n+ (as shown in Figure 2C). TheL a-La distance is decreased from LaOI (7.28 )t oL aOBr (5.80 )t oL aOCl (5.29 )a nd LaOF (4.40 ).…”

“…[3,23] Figure S8 in the Supporting Information shows powder XRD data for LaOCl, LaOBr, and LaOI nanocrystals incorporating Tb 3+ on La-sites prepared by metathesis reactions of Tb x La 1Àx OI nanocrystals as per Equation (3). Figure S8B shows amonotonic shift of the (002) reflections to higher 2q values reflecting the closer interplanar separation of the (LaO) n n+ blocks [32] in going from the LaOI to LaOF with retention of the matlockite crystal structure.B ased on ICP-MS measurements,the Tb:X ratio remains almost unchanged at 0.08 upon topotactic reaction suggesting preservation of the cation sublattice.While the green coloration characteristic of the Tb 3+ chromophore is retained, Figure S9 in the Supporting Information shows PL excitation and emission data as well as aCommission International de IEclairage (CIE) chromaticity plot for the topochemically transformed oxyhalide nanocrystals illustrating ablue shift of the excitation band and red shift of the 5 D 4 ! 7 F 5 emission band in going up the halide group.…”

Halide Replacement with Complete Preservation of Crystal Lattice in Mixed‐Anion Lanthanide Oxyhalides

“…In the LaOI structure, a probable pathway for halide‐ion diffusion is along the ab plane [32] along the halide slab that separates infinite fluorite‐type blocks of (LaO) n n + (as shown in Figure 2 C). The La‐La distance is decreased from LaOI (7.28 Å) to LaOBr (5.80 Å) to LaOCl (5.29 Å) and LaOF (4.40 Å).…”

Oxidation State and Local Structure of Chromium Ions in LaOCl

“…Lanthanum oxychloride (LaOCl), which is being considered for a variety of applications including gas sensors [1][2][3][4][5][6][7][8], catalysts [9][10][11], and solid electrolytes [12][13][14], is one of the most widely investigated compounds from the class of lanthanide oxyhalides. Historically, LaOCl has been primarily studied as a host matrix for rare-earth ions to establish the systematics of fluorescence spectra transition interrelations with crystal field parameters [15][16][17][18][19].…”

“…The larger Eu 2+ ions expand the lattice and require charge compensation, possibly in the form of Cl − ion vacancies [34]. The introduction of divalent cations, such as Ca 2+ and Mg 2+ , is likely to produce lattice defects in LaOCl which can improve the optical [29] or electrical [13] properties of the material. Studies of Sb [46,47] and Bi [48] doped LaOCl are especially interesting as the luminescence spectra showed the presence of two emission centers, while there is only one evident crystallographic site for substitution.…”