Apatite germanates doped with tungsten: synthesis, structure, and conductivity

Abstract

High oxygen content apatite germanates, La 10 Ge 6-x W x O 27+x , have been prepared by doping on the Ge site with W. In addition to increasing the oxygen content, this doping strategy is shown to result in stabilisation of the hexagonal lattice, and yield high conductivities. Structural studies of La 10 Ge 5.5 W 0.5 O 27.5 show that the interstitial oxygen sites are associated to a different degree with the Ge/WO 4 tetrahedra, leading to five coordinate Ge/W and significant disorder for the oxygen sites associated with these units.Raman spectroscopy studies suggest that in the case of the WO 5 units, the interstitial oxygen is more tightly bonded and therefore not as mobile as in the case of the GeO 5 units, thus not contributing significantly to the conduction process.2

Sr2(Mg1−Ga )Ge2O7+0.5: Melilite-type oxygen ionic conductor associated with fivefold coordinated germanium and gallium

“…Appearance of the characteristic Raman band around 650 cm À1 corresponding to the stretching mode of GeeO in GeO 5 unit experimentally supports the existence of the interstitial oxygen bound to Ge in Sr 2 (Mg 1Àx Ga x )Ge 2 O 7þ0.5x with x ¼ 0.2 and 0.5 as shown in Fig. S6 [21,22].…”

Effects of La content on the densification, microstructure, and conductivity of doped La10−xGe6O26±δ electrolytes

“…However, lanthanum germanate apatites often encounter the downside of GeO 2 volatilization at high temperatures, leading to the formation of another conducting phase, La 2 GeO 5 . It has been reported in the literature that a triclinic apatite phase exists in the La‐Ge‐O phase diagram . Leon‐Reina et al .…”

“…13,15 It has been reported in the literature that a triclinic apatite phase exists in the La-Ge-O phase diagram. 16,17 Leon-Reina et al found that La 9.33+x (GeO 4 ) 6 O 2+3x/2 samples with a composition of 0.19≤x≤0.27 were marked with hexagonal symmetry, while those with a higher La content of 0.33≤x≤0.42 exhibited a triclinic cell, which leads to more strongly bound oxygen, and results in reduced conductivity. 2 Nakayama et al reported that the electrical conductivities of La x (GeO 4 ) 6 O 1.5xÀ12 depend on the La content; they found that La 9.0 (GeO 4 ) 6 O 1.5 had the highest conductivity among various La x (GeO 4 ) 6 O 1.5xÀ12 apatites.…”

“…15,18 There have been several doping studies on lanthanum germanates. 8,16,[18][19][20][21][22][23][24] In our previous study, the structures and electrical conductivities of La 9.5 Ge 5.5 Me 0.5 O 26AEd (Me: Mg, Al, Ga, Sn, Fe, Mn, Ti, Ni, Mo, Nb, and W) were examined. [25][26][27] Although all the germanates were densified at temperatures below 1500°C, aliovalent doping of Nb, W, and Mo on the Ge site marked with the highest electrical conductivity among the compositions evaluated.…”

Vanadium-doped and mixed Si/Ge-based apatites : synthesis, crystal chemistry and ionic conductivity

“…where A are rare-earths or alkaline-earths and B is Si or Ge. Apatites contain several cation acceptor sites leading to a wide range of substitutional possibilities [53][54][55][56][57][58][59][60][61][62][63][64][65][66][67] with ion mobility modified by varying cation type and proportions.…”