ASIAN JOURNAL OF PHYSICS

Brief Theme

With the advent in nanoscience and nanotechnology a new class of material namely functional oxides is emerging. Functional oxide (FO) refers to the metal oxides in the nanodimensions regime exhibiting novel, interesting and superior functions owing to their high surface area to volume ratios and related properties. More specifically, FO has two structural characteristics: cations with mixed valencies and anions with deficiencies or vacancies. Both these characteristics can easily be tuned by controlling the dimension of the material. As the functions of the material are closely related to its structure and morphology, a precise control over the process parameters can be looked upon as a tool to fabricate designer materials for next generation smart device applications. Advances in the nanosciences have demonstrated that FO having wealth of interesting morphologies and exhibiting interesting and novel structure-property relationship can easily be synthesized. Some of the FO’s that have shown interesting and promising properties are ZnO, SnO₂, CdO, CaO, Ga₂O₃, TiO₂, CuO, MoO₃, CeO₂ and In₂O₃. FO’s have exhibited novel and improved properties, in almost every subject or areas like semiconductivity, magnetism, optics, ferroelectrocity, piezoelectricity, superconductivity, thermoelectricity and catalysis. Accordingly, they have found applications in various fields like solar cells, thermoelectrics, photocatalysis and gas sensing.

            For gas sensing applications the ability to synthesis FO with tailored made surface reactivity have resulted in sensors with enhanced sensor response characteristics. The sensors are required to fulfill the 4S selection criteria namely “Sensor response, Selectivity, Stability and Suitability”. For successful deployment, the sensor should exhibit high sensor response, high selectivity towards a particular gas, long term stability in the test environment and should be economically viable. Different FO’s like SnO₂, ZnO, WO₃, and In₂O₃ have demonstrated their potential in fulfilling the above mention selection criteria and accordingly, sensor for industrial, agriculture and biomedical applications have been realized. Example can be provided of ZnO nanowires wherein the operating temperature of maximum sensor response was systematically brought down to room temperature by a careful choice of sensitizers. The nanowires were synthesized using hydrothermal method which is also an economical viable process.

            For thermoelectric applications i.e., scavenging waste heat and converting it into electricity, FO are expected to play an important role. The conversion efficiency of a thermoelectric material is evaluated according to its figure of merit, defined as Z = S²σ/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, and κ is the thermal conductivity. Herein FO material offers the advantages like high thermal stability, low cost, and weak toxicity. Some complex superlattices in nanostructures contain periodic compositional and structural features, typically on the nanometer scale, making them promising materials for thermoelectric applications. In particular, the nano dimension of the material helps in the significant reduction of the thermal conductivity owing to the scattering of a wide spectrum of phonons by dislocations, nanoscale amorphous/crystalline features and grain boundaries. This eventually is expected to contribute for increasing the ZT of the material.

            For photovoltaic applications, FO’s have found their utility as transparent conducting front electrodes in solar cells and as electron or hole transport layers. More recently, heterojunctions entirely based on FOs, so called all-oxide photovoltaic cells (TiO₂/Cu₂O, ZnO/Cu₂O), are attracting considerable attention due to their promising potential for price reduction. Apart from this FO have demonstrated their utility for other energy applications like batteries, solid-oxide fuel cells and photo catalysis.

                The special issue aims at providing an introduction to the novel and emerging field of functional oxides. More specifically, it will provide an overview of different synthesis approaches, characterization, properties and applications of commonly used functional oxides like ZnO, SnO₂, CdO, CaO, Ga₂O₃, TiO₂, CuO, MoO₃, CeO₂ and In₂O₃. The physics and chemistry at nanoscale highlighting the nano size effects, interface properties, structure-property relation and integrated functionalities will also be addressed. The issue will also emphasis the applied aspects of physics, chemistry and engineering of FO’s for their possible usage in applications including sensors, thermoelectrics, solar cells, photocatalysis and micro/nano electronics. In particular, the issue will cover the recent advances in the next generation device application of these materials with main emphasis on the challenges that are required to be met in order to achieve or realize the complete commercial product.

Last date of Submission of Manuscript: 30^th January 2016.