P. Padmini

Improved ferroelectric property of LaNiO3/Pb(Zr0.2Ti0.8)O3/LaNiO3 capacitors prepared by chemical solution deposition on platinized silicon

We report a technique to prepare top and bottom oxide electrodes of LaNiO3 (LNO) for lead zirconate titanate (PZT) films using a chemical solution deposition. LNO/PZT/LNO sandwich structures were prepared on platinized silicon by spin coating combined with rapid thermal annealing. Pt dots were sputtered on top of LaNiO3 film to serve as protective masks during etching of the uncovered LaNiO3 layer using dilute hydrochloric acid. For comparison, Pt/PZT/Pt capacitors were also prepared using the same processing conditions. Electrical measurements were carried out on both Pt/LNO/PZT/LNO/Pt and Pt/PZT/Pt structures. The remnant polarizations and coercive fields for these two capacitors are 17.4 and 21.4μC∕cm2, 71 and 81.5kV∕cm respectively at 5V. The leakage current density for the Pt/LNO/PZT/LNO/Pt structure is about 1.38×10−6A∕cm2 at 5V, which is lower than that of PZT deposited on Pt electrode. After 109 bipolar switching cycles, no significant change in remnant polarization was observed in the Pt/LNO/PZT/...

Highly a-axis-oriented Nb-doped Pb(TixZr1−x)O3 thin films grown by sol–gel technique for uncooled infrared dectors

Pb(Nb0.02Zr0.2Ti0.8)O3 thin films with thickness of 900nm were spincoated on platinized silicon substrate using the sol–gel method. X-ray diffraction and field emission scanning electron microscopy show that the films are highly a-axis-oriented with columnar structure. A large remnant polarization (Pr+) ∼92.2μC∕cm−2 was observed for as-grown films. The coercive field (Ec+) for these films was 159.3kV∕cm. Good pyroelectric properties are obtained as a result of large remnant and spontaneous polarization and their strong temperature dependence. The pyroelectric coefficient and figure of merit at room temperature (22°C) are 10.8×10−4Cm−2K−1 and 2.34×10−5Pa−1∕2, respectively.

Preparation and characterization of epitaxial ilmenite-hematite films

The solid solution system ilmenite-hematite [(FeTiO3)1−x–(Fe2O3)x] is a potential candidate for applications in spintronics due to its intrinsic ferrimagnetic and semiconducting properties. Epitaxial ilmenite-hematite films with x=0.33, which have the highest room temperature magnetic moment, were grown on α-Al2O3 (0001) substrates using pulsed laser deposition technique with varying oxygen partial pressure in the ambient gas. Structural, magnetic, electrical, and optical properties are found to be largely dependent on the oxygen content of the films which is controlled by substrate temperature and ambient gas composition. The highest crystalline and magnetic ordering and the lowest resistivity values could be obtained for growth at high temperatures and under low oxygen pressure. A narrowing of the band gap (to around 2.4eV) was observed for films grown under high oxygen pressure in comparison with films grown in vacuum or argon (around 3.3eV).

Chemical ordering in ilmenite-hematite bulk ceramics through proton irradiation

We demonstrated the capability of MeV proton irradiation to promote chemical ordering processes in a solid at low temperature. We used the ilmenite–hematite solid solution system which allows estimation of the degree of ordering through measurement of its magnetization. Normally, ordering through diffusion would require high temperature annealing. At high temperatures, however, the equilibrium state would be less ordered and thus the achievable ordering incomplete. High energetic protons continuously transfer energy to the sample through electronic interaction which locally deposits large quantities of energy without a general increase of the sample temperature. This promotes diffusion processes which allow the system to relax towards the ordered equilibrium state.

Neutron radiation effects on the nonlinear current–voltage characteristics of ilmenite-hematite ceramics

Ilmenite-hematite (IH) is a wide-band gap semiconducting material with a potential for low-voltage varistor applications. The nonlinear characteristics of this material were investigated before and after exposure to high-energy neutron radiation. The typical current–voltage characteristics of a varistor device are retained in all our samples subjected to neutron radiation. However, the effect is more pronounced on the device parameters like the nonlinear coefficient (α) and switching field (Es). The crystallinity of the ceramic remains unaffected after irradiation. Our observations confirm that IH-based varistor devices can perform satisfactorily even in radiation dominant environments such as in space and nuclear reactors.

Magnetic properties of ilmenite-hematite films and bulk samples

Ilmenite-hematite [(FeTiO3)1−x–(Fe2O3)x] is a solid solution system with intrinsic ferrimagnetic and semiconducting properties. Bulk ceramic samples and epitaxial thin films have been prepared with magnetization values of up to 1500G (bulk) and 700G (thin films) at room temperature. Superparamagnetic behavior was discriminated from ferrimagnetic properties using field cooled and zero field cooled measurements. The blocking temperature exceeds room temperature for samples with composition x>0.25. Using magnetic force microscopy, the domain structure in the thin ilmenite-hematite films was detected.

Integrated PNZT Structures for MEMS Gyroscope

The effect of processing on the ferroelectric and piezoelectric properties of sol-gel grown Pb1.1Nb0.04Zr0.2Ti0.8O3 (PNZT) thin films was investigated. The effective d 31 piezoelectric coefficient of as-grown films was measured using piezoelectrically actuated cantilevers. The results indicate that films annealed after each layer possess a significant internal field, leading to high piezoelectric coefficients in the as-grown PNZT films. But the films annealed in the final step possess a very small internal field, and, consequently, small piezoelectric response.

IV and CV Characteristics of Multifunctional Ilmenite-Hematite 0.67FeTiO3-0.33Fe2O3

We investigated the IV and CV properties of an [(FeTiO3)0.67 (Fe2O3)0.33] epitaxial thin film. The four point probe (4pp) measurements revealed that the material has a linear IV relation and has a resistivity of approximately 0.56 ω cm. In contrast, the two point (2pp) measurements are highly non-linear suggesting the existence of Schottky barriers. The CV data suggest that the material under the contacts is depleted. From the corrected CV data, the carrier concentration is found to be of the order of 1023/cm3.

Magnetic-Semiconductors in Fe-Ti-Oxide Series and Their Potential Applications

Multifunctional nature of the Fe-Ti-oxides makes them attractive candidates for novel applications in which their coupled semiconductor, magnetic, dielectric and optical properties can be exploited. In particular, they appear to be good candidates for the emerging technologies such as spintronics, magneto-electronics, and radhard electronics. In this paper we deal mostly with pseudobrookite (Fe2 TiO5), both pure and Mn-substituted variety. Materials processing, structural, magnetic and semiconducting properties have been discussed in-depth. The temperature and magnetic field dependence on the non-liner I-V characteristics are established opening the possibilities for fabricating magnetically switched devices