CTE Cr substitution Hebb-Wagner measurements La-doped SrTiO3 Mössbauer Ni-Cr-ferrite Ostwald ripening Solid Oxide Fuel Cells TEC Wulff shape aliovalent substitution ball milling binary fluorides bismuth vanadate cation mixing ceria chemical expansion coupled/decoupled ionic transport current collector e-beam physical vapor deposition electronic conductivity high temperature proton conductors hydration impedance spectroscopy impregnation ionic conductivity lanthanum orthoniobate magnetic properties metal foam molten salt synthesis