Nanostructured NiO samples having different average particle sizes were prepared and the variations of the real and imaginary components of the complex dielectric function epsi* were studied as a function of the frequency of the applied signal and temperature. The dielectric relaxation mechanism is discussed considering nanostructured NiO as a carrier dominated dielectric with high density of hopping charge carriers. The observed ohgrn – 1 dependence of the real and imaginary components of epsi* is discussed in the light of the 'Universal' model of dielectric response. The various contributions to the measured dielectric loss epsiPrime such as the steady state charge transport, delayed readjustment of screening charges and the Debye delays are discussed. It is shown that the temperature dependence of both the real and imaginary components of epsi* are in accordance with the models used for discussing the dielectric relaxation and loss mechanisms. The variation of epsiprime with average particle size seems to be rather complex depending on a number of parameters associated with the interfacial region which vary with the average particle size.

Li and Ti co-doped NiO thin films of 250 nm in thickness were deposited onto Pt/Ti/SiO2/Si(100) substrates using a sol-gel spin-coating method. The effect of Li doping content on microstructure and dielectric properties of the LixTyNi1-x-yO thin films in which the Ti content was fixed at 2 and 20 at% was investigated. All the thin films consisted of a mixture of NiO, NiTiO3, Li2NiO2 and/or LiNiO2 phases and show the high dielectric constant ranged from 235-370 in 100 Hz depending on the proportion of various phases. Excess Li content which results in increasing Li2NiO2 and the formation of LiNiO2 led to decrease the dielectric constant especially for the 2% Ti containing thin films in 100 Hz. The increased NiTiO3 and Li-dissolved Ni(Li)O phases by increasing Ti content from 2 to 20 at% is more beneficial for the formation of the core-shell like microstructure and hence enhancing the dielectric constant. However, the frequency stability of the dielectric constants was lowered by the formation of the excess NiTiO3 phase as Ti content was increased from 2 to 20 at%. The doping content of Li and Ti is necessary to control in an appropriate range in order to obtain the high dielectric property.

Amorphous model structures of hafnium aluminate having a Hf content of 0.2 (a-Hf0.2Al0.8O1.6), alumina (a-Al2O3), and hafnia (a-HfO2) are theoretically generated, and dielectric responses of the amorphous model structures are studied by the first-principles method. The models have corner, edge, and face shared AlOn (n=4–6) and HfOn (n=5–8) polyhedra, and the a-Hf0.2Al0.8O1.6 model structures are phase separated at the atomistic level, having Al2O3 and HfO2 domains. Calculated dielectric constants of the models increase with increasing Hf content, and the dielectric constant increase is dominated by the lattice polarization contribution to the dielectric constant. We found that low-frequency phonon modes having a frequency less than 200 cm−1 largely contribute to the high lattice dielectric constant and that inter-HfO2 domain vibrations and vibration of atoms in distorted metal-oxygen polyhedra are dominant in the modes.

We report the observation of extremely high dielectric permittivity exceeding 109 and magnetocapacitance of the order of 104% in La0.875Sr0.125MnO3 single crystal. This phenomenon is observed below 270 K, and it exhibits a history dependence. These effects may be the consequence of strong competition and interplay among the charge, orbital, and spin degrees of freedom, resulting in nanoscale charge and spin dynamic inhomogeneities in the prepercolation regime of the phase segregation.

KxTiyNi1-x-yO(x = 0.05–0.3, y = 0.02–0.25) ceramics (abbreviated as KTNO) have been synthesized showing high permittivity. All the KTNO samples of varying compositions exhibit high dielectric permittivity (~104) near room temperature, which is comparable to that of the recently discovered CaCu3Ti4O12 (CCTO) ceramic. The high dielectric constant of KTNO depends on both the K and Ti content and can be attributed to the Maxwell–Wagner polarization mechanism and to a thermally activated mechanism.

The authors present a first principles approach for investigating the dielectric properties of Cu-phthalocyanine (CuPc). The local position-dependent dielectric constant of CuPc oligomers is determined from the charge density induced by an external finite electric field. The dielectric constants of a CuPc monomer along and perpendicular to its plane are extracted from appropriately chosen periodic arrangements of CuPc oligomers. The authors obtain dielectric constant values of about 15 along the CuPc plane and about 3.4 perpendicular to the plane.

Feliciano Giustino, Angelo Bongiorno and Alfredo Pasquarello

P. Umari, A. J. Willamson, Giulia Galli, and Nicola Marzari

Feliciano Giustino and Alfredo Pasquarello

A.V.Shytov, P.B.Allen