S. C. Purandare

Scanning probe imaging of coexistent ferromagnetism and ferroelectricity at room temperature

Room temperature coexistence of ferromagnetism and ferroelectricity in a thin film of nominal composition PbTi0.5Fe0.5O3−δ is probed by standard ferroelectric and ferromagnetic hysteresis loop measurements and by scanning probe microscopy. Both magnetic domains and ferroelectric domains are observed in the same spatial region of the material, implying phase coexistence in this system. Sample morphology strongly affects the roughness of the domain walls for both order parameters.

Dielectric properties of oriented thin films of PbZrO3 on Si produced by pulsed laser ablation

PbZrO3 is an antiferroelectric perovskite with TC≈230 °C. We have deposited single phase, perfectly c-axis oriented thin films of PbZrO3 on Si(100) substrates by pulsed laser ablation at 700 °C. The growth conditions (substrate temperature, ambient oxygen pressure, and laser energy density) have been optimized and the morphology of the films studied by scanning electron microscopy and atomic force microscopy. From a study of the dielectric hysteresis of the films and a measurement of the temperature dependence of their capacitance, we find that films thicker than ≈300 nm are antiferroelectric, while thinner films (<300 nm) appear to exhibit ferroelectric behavior.

c‐axis oriented ferroelectric thin films of PbTiO3 on Si by pulsed laser ablation

We have deposited single phase c‐axis oriented ferroelectric thin films of PbTiO3 on Si(100) by pulsed laser ablation technique in situ. It has been shown that the formation of a nonferroelectric, Pb2Ti2O6 pyrochlore phase at the interface could be avoided by raising the substrate temperature.

Ferroelectric thin films of PbTiO3 on silicon

The advantages offered by ferroelectric films deposited directly onto silicon in memory applications, field effect devices and pyroelectric detectors have stimulated intense research activity. This review covers work carried out during the last several years on their growth, characterization and device fabrication using ferroelectric thin films of on single-crystalline Si substrate with and without buffer layers.

SILVER DOPING AND ITS INFLUENCE ON THE OXYGENATION DURING IN SITU GROWTH OF YBA2CU3O7-X THIN FILMS

The influence of Ag doping on both oxygenation and deoxygenation during growth of YBa2Cu3O7−x films at 700 °C by pulsed laser deposition has been studied. Experiments show that undoped and Ag‐doped films grown at 200 mTorr oxygen pressure and quenched immediately after termination of growth have a superconducting transition temperature Tc of 61 and 86 K, respectively. The high Tc of 86 K obtained with quenched Ag‐doped films is thought to be due to both enhanced oxygen incorporation and reduced deoxygenation associated with Ag doping. These results show that Ag‐doped YBa2Cu3O7−x films could be crucial for realizing devices based on multilayer structures.

PULSED LASER ABLATION : A NEW ROUTE TO SYNTHESIZE NOVEL SUPERCONDUCTING COMPOUNDS AS ORIENTED FILMS

We report here the significance of the pulsed laser ablation technique in stabilizing strained lattices that do not form by the conventional ceramic method and show that the technique offers unique possibilities to probe the structure property relationship in complicated systems. One of such systems is LuBa2Cu3O7−δ; a systematic investigation of structural (in)stability of its superconducting phase is presented here. Our analysis suggests that the system suffers from internal strain due to lower ionic radius of Lu3+; however, the structure can be stabilized only as oriented films on 〈100〉 LaAlO3, 〈100〉 SrTiO3, and 〈100〉 MgO, with excellent superconducting properties (Jc≊5.0×106 A cm−2 at 77 K). We have also investigated similar compounds having their stability close to their crystallographic limit. The important feature of these metastable phases is that they grow only as oriented films. Free energy of epitaxial growth of strained films are investigated and a simple growth model is proposed based on our o...

Breakthrough in densification of ferroelectric PbTiO3 with Si as sintering aid

Abstract We have successfully shown that Si acts as a sintering aid for PbTiO3. It is possible to achieve +95% of the theoretical single crystal density without hot pressing, using 2 mol% of Si as an additive. Si acts as a binder in the matrix and prevents crumbling of the sample by sustaining the large strain developed during phase transformation while cooling. Moreover, the presence of Si does not affect the crystal structure and tetragonality of PbTiO3 and thereby helps to retain the physical properties of the material. Availability of highly dense PbTiO3 samples in required shapes and sizes will help in exploration of the excellent ferroelectric and pyroelectric properties of PbTiO3.

Si induced size effects in ferroelectric PbTiO3

Physical properties of PbTiO3 in the presence of Si are investigated in detail. Polycrystalline bulk samples with nominal composition of (Pb1−xSix) (Ti1−xSix)O3, where x varies from 0.01 to 0.25, are synthesized using the coprecipitation route. The presence of Si in the matrix leads to a reduction in coherently diffracting domain size (dXRD). The observed reduction in the ferroelectric distortion in the lattice c/a, ferroelectric transition temperature Tc and shift in Raman lines of PbTiO3 with increase in Si content are attributed to the Si induced finite size effect. However, at higher calcination temperatures, the material exhibits properties similar to pure, undoped, bulk PbTiO3. There is no evidence of change in crystal structure and ferroelectric nature of PbTiO3 due to the presence of Si. Our data suggests that Si, which is diffused out of PbTiO3 perovskite lattice, is likely to reside in the grain boundary region in an as yet unidentified chemical form.

GROWTH AND MICROSTRUCTURAL STUDY OF RADIO-FREQUENCY MAGNETRON SPUTTERED MGO FILMS ON SILICON

Microstructure of magnesium oxide films radio frequency (rf) sputtered on 〈100〉 silicon substrates at various argon: oxygen (9:1) gas pressures in the range 1–6.7 Pa and at various substrate temperatures up to 700 °C have been studied using x‐ray diffraction and scanning electron microscopy. The films have shown a tendency for oriented structure with growth orientation perpendicular to the 〈200〉 planes. The tendency for columnar growth has been found to be strong at high argon pressures and has been found to persist to higher substrate temperatures. This observation is consistent with the structure zone model proposed by Movchan and Demchishin [Phys. Met. Mettallogr. 28, 83 (1969)] and later studied by Thornton [J. Vac. Sci. Technol. 11, 666 (1974)]. Annealing of films at 900 °C in oxygen which is needed to reduce oxygen deficiencies and strain generated during growth, and to improve crystallinity by increasing grain size, has been found to cause microcracks in the films depending upon the microstructure ...

Microstructural studies of aqueous sol derived ferroelectric PbTiO3 thin films

Aqueous sol derived ferroelectric PbTiO3 thin films have been deposited on Si(100) substrates. Films crystallized by annealing at 675 °C, which exhibit the best ferroelectric properties and also excellent varistor-type behaviour, have been investigated in detail by TEM and x-ray diffraction. There is a partially preferred orientation of the crystallized grains of the perovskite phase along the (110) and (101) directions. During annealing, Si from the substrate diffuses into the films and forms an amorphous Si-O rich phase at the boundaries of the equiaxed grains of the perovskite phase. The formation of this amorphous phase is expected to increase the resistivity of the grain boundaries and consequently promote varistor-type behaviour. Domains were observed within the equiaxed grains and they exhibited a needle-like morphology. In a single grain, either a set of parallel domains or two sets of differently oriented parallel domains were observed. With increased diffusion of Si from the substrate, the fraction of the amorphous phase in the microstructure increased. The amorphous phase penetrated the domain boundaries within a single grain, eventually isolating the needle-like domains. The resulting microstructure consisted of needles of the perovskite phase in an amorphous matrix.