Quest for lead free relaxors in YIn(1-x)Fe(x)O3 (0.0 ≤ x ≤ 1.0) system: role of synthesis and structure.

The B-site tailored YIn(1-x)Fe(x)O3 (0.0≤ x≤ 1.0) series was synthesized by glycine-aided gel-combustion technique and subjected to extensive structural and electrical investigations. The temperature had tremendous bearing on the phase evolution exhibited by the system. The entire system crystallized as C-type metastable polymorph in the as-synthesized form. Hexagonal polymorphs of Fe(3+)-rich compositions could be isolated by controlled heat treatment at 750 °C. Raman spectroscopic investigations showed that, while there is a general shrinkage of the lattice due to substitution of a smaller ion at In(3+)-site, there is an apparent dilation of the Y-O bond, and this anomaly reflects in the electrical behavior exhibited by the system. The single-phasic hexagonal nominal compositions, YIn(1-x)Fe(x)O3 (0.0 ≤ x ≤ 0.3), were also studied by impedance spectroscopy. The dielectric constant was found to drastically increase from 10 for YInO3 to 1000 for YIn(0.7)Fe(0.3)O3 at room temperature stressing the role of B-site tailoring on electrical behavior. More interestingly, careful substitution of Fe into YInO3 could tune the electrical behavior from a dielectric to relaxor ferroelectric in the temperature range studied. The nominal composition YIn(0.7)Fe(0.3)O3 showed a classical relaxor ferroelectric like behavior which is an important observation in context of the search for new lead free relaxor materials.

Synthesis and structural and electrical investigations of a hexagonal Y(1-x)Gd(x)InO3 (0.0 ≤ x ≤ 1.0) system obtained via metastable C-type intermediates.

Detailed structural and electrical investigations were carried out on an A-site disordered hexagonal Y(1-x)Gd(x)InO3 (0.0 ≤ x ≤ 1.0) series synthesized by a self-assisted gel-combustion route. The phase relations show profound temperature dependence. The metastable C-type modification could be stabilized for all the compositions, which on further heating get converted to stable hexagonal polymorphs. The conversion temperature (C-type to hexagonal) was found to increase with an increase in Y(3+) content. The system was observed to be single-phasic hexagonal at 1250 °C throughout the composition range. Interestingly, the increase in planar bonds of InO5 polyhedra was found to be twice that of the apical bonds on Gd(3+) substitution. Careful Raman spectroscopic studies highlighted a definitive though subtle structural change from x = 0.7 onward. The same observation is also corroborated by the dielectric studies. Electric field-dependent polarization measurements showed the ferroelectric hysteresis loop for pure YInO3. The system transforms from ferroelectric in YInO3 to almost paraelectric for GdInO3. In the present study, XRD, Raman, and electrical characterizations in conjunction reveal that to tune the electrical properties of the hexagonal rare earth indates, the variation in tilting of InO5 polyhedra has to be influenced, which could not be brought about by isovalent A-site substitution.

Grain size effect on the radiation damage tolerance of cubic zirconia against simultaneous low and high energy heavy ions: Nano triumphs bulk.

Irradiation induced damage in materials is highly detrimental and is a critical issue in several vital science and technology fields, e.g., the nuclear and space industries. While the effect of dimensionality (nano/bulk) of materials on its radiation damage tolerance has been receiving tremendous interest, studies have only concentrated on low energy (nuclear energy loss (Sn) dominant) and high energy (electronic energy loss (Se) dominant) irradiations independently (wherein, interestingly, the effect is opposite). In-fact, research on radiation damage in general has almost entirely focused only on independent irradiations with low and/or high energy particles till date, and investigations under simultaneous impingement of energetic particles (which also correspond to the actual irradiation conditions during real-world applications) are very scarce. The present work elucidates, taking cubic zirconia as a model system, the effect of grain size (26 nm vs 80 nm) on the radiation tolerance against simultaneous irradiation with low energy (900 keV I) and high energy (27 meV Fe) particles/ions; and, in particular, introduces the enhancement in the radiation damage tolerance upon downsizing from bulk to nano dimension. This result is interpreted within the framework of the thermal-spike model after considering (1) the fact that there is essentially no spatial and time overlap between the damage events of the two 'simultaneous' irradiations, and (2) the influence of grain size on radiation damage against individual Sn and Se. The present work besides providing the first fundamental insights into how the grain size/grain boundary density inherently mediates the radiation response of a material to simultaneous Sn and Se deposition, also (1) paves the way for potential application of nano-crystalline materials in the nuclear industry (where simultaneous irradiations with low and high energy particles correspond to the actual irradiation conditions), and (2) lays the groundwork for understanding the material behaviour under other simultaneous (viz. Sn and Sn, Se and Se) irradiations.

Rare earth indates (RE: La-Yb): influence of the synthesis route and heat treatment on the crystal structure.

Rare earth indates are an interesting class of compounds with rich crystallography. The present study explores the crystallographic phases observed in REInO3 (RE: La-Yb) systems and their dependence on synthesis routes and annealing temperature. All REInO3 compositions were synthesized by a solid state route as well as gel-combustion synthesis (GC) followed by annealing at different temperatures. The systems were well characterized by powder XRD studies and were analysed by Rietveld refinement for the structural parameters. The cell parameters were observed to decrease in accordance with the trend in ionic radii on proceeding from lighter to heavier rare earth ions. Interestingly, the synthesis route and the annealing temperature had a profound bearing on the phase relationships observed in the REInO3 series. The solid state synthesized samples depicted an orthorhombic phase (Pbnm) field for LaInO3 to SmInO3, followed by a hexagonal-type phase (P63cm) for GdInO3 to DyInO3. However, the phase field distribution was greatly influenced upon employing gel-combustion (GC) wherein both single-phasic hexagonal and orthorhombic phase fields were found to shrink. Annealing the GC-synthesized compositions to still higher temperatures (1250 °C) further evolved the phase boundaries. An important outcome of the study is observance of polymorphism in SmInO3 which crystallized in the hexagonal phase when synthesized by GC and orthorhombic phase by solid state synthesis. This reveals the all-important role played by synthesis conditions. The existence and energetics of the two polymorphs have been elucidated and discussed with the aid of theoretical studies.

Nano-cerium vanadate: a novel inorganic ion exchanger for removal of americium and uranium from simulated aqueous nuclear waste.

Cerium vanadate nanopowders were synthesized by a facile low temperature co-precipitation method. The product was characterized by X-ray diffraction and transmission electron microscopy and found to consist of ∼25 nm spherical nanoparticles. The efficiency of these nanopowders for uptake of alpha-emitting radionuclides (233)U (4.82 MeV α) and (241)Am (5.49 MeV α, 60 keV γ) has been investigated. Thermodynamically and kinetically favorable uptake of these radionuclides resulted in their complete removal within 3h from aqueous acidic feed solutions. The uptake capacity was observed to increase with increase in pH as the zeta potential value decreased with the increase in pH but effect of ionic strength was insignificant. Little influence of the ions like Sr(2+), Ru(3+), Fe(3+), etc., in the uptake process indicated CeVO4 nanopowders to be amenable for practical applications. The isotherms indicated predominant uptake of the radioactive metal ions in the solid phase of the exchanger at lower feed concentrations and linear Kielland plots with positive slopes indicated favorable exchange of the metal ions with the nanopowder. Performance comparison with the other sorbents reported indicated excellent potential of nano-cerium vanadate for removing americium and uranium from large volumes of aqueous acidic solutions.