Ho-doped BaTiO3: Polymorphism, phase equilibria and dielectric properties of BaTi1−xHoxO3−x/2: 0≤x≤0.17

Photoluminescence associated with the site occupations of Ho3+ ions in BaTiO3

“…Although at a high sintering temperature (e.g. T s  = 1550 °C 10, 15 ) Ho 3+ ions are considered to substitute for the Ti sites, even at a lower T s Ho 3+ ions inevitably enter the Ti sites in part, as observed in Fig. 3c.…”

“…Barium titanate (BaTiO 3 ) is a typical dielectric material. The dielectric properties and structural information of Ho-doped BaTiO 3 were systematically investigated in terms of structural modification 9–15 . Ho 3+ is known to be an amphoteric dopant in BaTiO 3 polycrystalline ceramic and its solid solubility is dependent on the Ba/Ti ratio and sintering temperature ( T s ).…”

“…Higher T s is generally required for the incorporation of Ho 3+ into the Ti site because of a relatively larger ionic size of Ho 3+ compared to Ti 4+ (Table 1) 16 and TiO 6 octahedrons characteristic of the skeleton of the perovskite structure. In the Ba-rich case, the solubility limit was reported to be x  = ~15% at T s  = 1550 °C and the formula was described as Ba(Ti 1− x Ho x )O 3− x /2 with O vacancies 10, 14, 15 . However, Ti vacancies and O ones had not been confirmed in Ho-doped BaTiO 3 and one is hard to avoid questioning a single site-occupation mode due to the amphoteric nature of Ho 3+ .…”

A phenomenological model of conduction in Ho-doped barium titanate sensor

“…Larger ions prefer to replace barium ions which have a radius of 0.135 nm while smaller ions prefer to replace titanium ions with a radius 0.068 nm. The intermediate rare earth ions (Ho 3+ , Dy 3+ , Y 3+ , Er 3+ ) may occupy either Ba 2+ or Ti 4+ sites, depending on the Ba/Ti ratio and solubility [11][12][13][14]. Barium titanate doped with Ho 3+ ions, which have a radius of 0.0901 nm, with atomic composition Ba 1−x Ho x TiO 3 exhibit maximum n-type conductivity at x = 0.3 mol%.…”

“…Barium titanate doped with different molar fractions of Ho 2 O 3 has been studied by many workers [14][15][16][17][18][19]. It has been mentioned earlier that barium titanate doped with holmium concentration of 0.3 mol% exhibits maximum conductivity at room temperature [15].…”