Direct view at colossal permittivity in donor-acceptor (Nb, In) co-doped rutile TiO2

Abstract

Topical observations of colossal permittivity (CP) with low dielectric loss in donor-acceptor cations co-doped rutile TiO2 have opened up several possibilities in microelectronics and energy-storage devices. Yet, the precise origin of the CP behavior, knowledge of which is essential to empower the device integration suitably, is highly disputed in the literature. From spectromicroscopic approach besides dielectric measurements, we explore that microscopic electronic inhomogeneities along with the nano-scale phase boundaries and the low temperature polaronic relaxation are mostly responsible for such a dielectric behavior, rather than electron-pinned defect-dipoles/grain-boundary effects as usually proposed. Donor-acceptor co-doping results in a controlled carrier-hopping inevitably influencing the dielectric loss while invariably upholding the CP value.

Influence of Zr dopant on polarization in rutile (In0.5Nb0.5)0.005(Ti1‐xZrx)0.995O2 ceramics

“…Spin‐orbit splitting of 2.7, 2.8 and 2.6 eV in samples with x = 0, 0.05 and 0.10, respectively, are consistent with the previously reported data, and confirm the presence of Nb 5+ in the prepared ceramics . Similarly, only In3d with an oxidation state of +3 in the prepared ceramics . The binding energies of Zr3d electrons in the x = 0.05 sample were 181.8 eV and 184.0 eV for 3d 5/2 and 3d 3/2 .…”

“…[8][9][10][11] Other mechanisms in the CP co-doped TiO 2 are also presented, such as Maxwell-Wagner polarization, which stems from the spatial heterogeneity of conductivity at the grain boundary (GBLC), interface (IBLC) and resistive outer surface (SBLC), and polaronic polarization caused by microscopic heterogeneities have been observed. 8,[11][12][13][14] These mechanisms coexist and are consistent with the defect-cluster model in co-doped TiO 2 . [15][16][17] In general, electrons in rutile (A 0.5 3+ B 0.5 5+ ) where C = A 3+ , Ti 3+ , or Ti 4+ ) in the TiO 2 lattice that correlated/ overlapped with each other.…”

“…44 Similarly, only In3d with an oxidation state of +3 in the prepared ceramics. 2,12,13,45 The binding energies of Zr3d electrons in the x = 0.05 sample were 181.8 eV and 184.0 eV for 3d 5 In general, substituting Nb 5+ for TiO 2 leads free electrons created by reducing Ti 4+ to Ti 3+ as follows:…”

Colossal Permittivity and Multiple Effects in (Zn + Ta) co-doped TiO2 Ceramics

“…Subsequently, a lot of doping modification of TiO2 based ceramics is carried out and the mechanism of its colossal dielectric effect is discussed [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. In addition to EPDD, other mechanisms have been proposed, including the IBLC effect, electrode effect [14,26], electron hopping [27], surface barrier effect [28], and micro-inhomogeneity and polarization relaxation [29]. Hence, the mechanism is still controversial.…”

Colossal permittivity in TiO2 co‐doped by donor Nb and isovalent Zr

“…[7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] Most of those reports are convinced of the formation of electronpinned defect-dipole (EPDD), while other mechanisms have also been proposed including interface effect arising from internal barrier layer capacitor (IBLC) effect, 10,22 electrode effect, 11 hopping conductivity, 23 surface barrier layer effect 24 and microscopic inhomogeneities and polaronic relaxation. 25 It seems a prerequisite to achieve CP and low dielectric loss via the simultaneous incorporation of acceptor and donor substitutions into TiO 2 , although the mechanism is still controversial.…”