Growth of Ba-Al- and K-Zn-Priderite Single Crystals by the FZ Method and Ionic Conductivities
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Large single crystals of Ba-Al-priderite (BATO) and K-Zn-priderite (KZTO) which are characterized by the one-dimensional tunnel structure with the hollandite type were grown by the floating zone (FZ) method. The chemical compositions, lattice parameters and melting temperatures of the obtained crystals are determined. BATO crystals melt congruently at 1510°C±10°C with a Ba1.18Al2.36Ti5.64O16 composition, and KZTO crystals at 1388°±10°C with a K1.56Zn0.75Ti7.25O16 composition. The frequency-dependence of complex ionic conductivities for BATO and KZTO single crystals was measured at room temperature. The BATO indicates complex behavior of a mixed conduction. The electronic conduction is predominant below 100Hz, but the ionic conduction becomes gradually predominant above 100Hz. The ac ionic conductivities of BATO and KZTO at 100kHz are 9.2×10-4S·cm-1 and 2.4×10-3S·cm-1, respectively.Cryptand
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Partial pressure
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Monoclinic crystal system
Partial pressure
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Ionic transport behaviors of silver chloride (AgCl) have been revealed with impedance spectra measurement under high pressures up to 20.4 GPa. AgCl always presented ionic conducting under experimental pressures, but electronic conduction can coexist with ionic conduction within the pressure range from 6.7 to 9.3 GPa. The ionic conductivity of AgCl decreases by three orders of magnitude under compression, indicating that Ag+ ion migrations are suppressed by high pressure. A parameter, fW, was defined as the starting frequency at which Ag+ ions begin to show obvious long-distance diffusion in AgCl. fW showed a similar trend with the ionic conductivity under high pressures, indicating that the speed of Ag+ ion diffusion slows down as the pressure increases. Unlike AgI, Ag+ ion diffusion in AgCl is controlled by the indirect-interstitial mechanism. Due to stronger ionic bonds and larger lattice deformation, Ag+ ion diffusion in the rigid Cl− lattice is more difficult than in the I− lattice under high pressures.
Silver chloride
Lattice diffusion coefficient
Lattice constant
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Ionic potential
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Dependence of the lattice parameter and Li+ ionic conductivity on the B-site ion substitution in perovskite-related compounds (Li0.1La0.3)yMxNb1 − xO3 (M = Zr, Ti, Ta) has been investigated. According to the calculation based on the classical ionic crystal model, ionic conductivity is expected to increase under the following two conditions: (i) a smaller average charge of B-site cations; and (ii) a larger unit cell. From the powder XRD results, Zr4+ substitution was satisfied with these two conditions. While in the case of Ti4+ substitution the former condition was satisfied, the latter one showed opposite tendency. In the case of Ta5+ substitution, both of the conditions are not changed. Therefore Zr4+-substituted samples were expected to increase the ionic conductivity. However, the ionic conductivity of all the B-site substituted samples decreased with the amount of substitution, in particular, Zr4+-substituted samples showed the lowest ionic conductivity. This disagreement indicates that there is an additional factor affecting the ionic conductivity. We suggest three possible explanations: (1) local distortion introduced by cation substitution; (2) the change of B–O bond covalency; and (3) formation of short-range ordering with B-site substitution.
Substitution (logic)
Formula unit
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