Design of Materials Laboratory

1. Novel Multiferroic Nanostructure of TMOs

Materials at smaller length-scales are capable of stabilizing novel phases with unique functionalities which in general, are not realized in bulk structures. Functionalities of nanocrystalline materials are dependent on their size, shape as well as crystallographic structure. Using a combination of hydrothermal synthesis technique, various characterization tools and ab-initio electronic structure calculations, we are exploring the new area of material designing for customized applications. In this connection our present interest lies on transition metal oxides owing to their susceptibility to external perturbations allowing a vast ground to combine different order parameters and study their inter-play:

(i) Gallium Ferrite (GFO) Nanostructure with P2₁2₁2₁symmetry

Hydrothermal synthesis of GFO nanostructure under controlled atmosphere demonstrates unique hexagonal bi-pyramid morphology with narrow size distribution. The sample possesses novel crystal structure (P2₁2₁2₁) different from the bulk (Pna2₁). The system shows a very weak magnetic moment of Fe ions, however, offers much reduced band gap interesting from the photochemical catalytic applications. The system demonstrates strong hydrophilic character and yields excellent dye degradation behaviour.

Collaborator: S. Mukherjee, CSIR-IMMT Bhubaneswar

Mishra et al. J. Mater. Chem. A ,2018,6, 13031

(ii) Gallium Ferrite (GFO) Nanostructure with R3c symmetry

High pressure studies on GFO predicts a number of phase transformations. Further process parameter alteration during hydrothermal synthesis yields a polar, perovskite phase of GFO. Rietveld refinement predicts Rhombohedral R3c symmetry. Estimated band-gap using optical absorption study and ab-initio calculations is ~ 2 eV. DFT study further predicts existence of two equivalent energy states suggesting evidence of ferroelectricity. Switching spectroscopy measurement confirms the same. Estimated polarization using Berry phase calculations is ~ 20-25 μC/cm². DFT calculations predicts a G-type antiferromagnetic order. Magnetic measurement shows weak magnetization with transition temperature beyond room temperature. Our study suggests that GFO with R3c symmetry demonstrates room temperature multiferroism.

Collaborator: S. Mukherjee, CSIR-IMMT Bhubaneswar

To be Submitted, 2019

(iii) Strontium Manganate (SMO) Nanostructure

Phase engineering in transition metal oxides is proven to be an effective design strategy for novel multiferroics. Our first-principles study on Strontium manganate (SMO) predicts Non-polar antiferromagnetic bulk symmetry (P6₃/mmc) to undergo a high pressure phase transformation to a polar and magnetically ordered tetragonal phase (P4mm) which is also ferroelectric. Initial hydrothermal synthesis produces a phase mixture of at least two different morphologies with small fraction of elongated one dimensional nanostructure. Rietveld refinement predicts the phase to be tetragonal P4mm. Magnetization measurement shows close-to-room temperature transition. Bulk electrical measurement hints ferroelectricity. However, further detailed characterization is underway to confirm ferroelectric nature. The system demonstrates comparatively small band gap, ~1.5 eV. Similar design strategies would be explored in other potential systems.

Collaborator: S. Mukherjee, S. Chatterjee CSIR-IMMT Bhubaneswar

P. Swarnakar, ICPCM-2018 at NIT Rourkela, India

2. Energy harvesting using Ferroic Materials

(i) Band-gap engineemultiferroics for solar photovoltaics

Ferroelectrics owing to their non-centrosymmetric crystal structure demonstrate spontaneous separation of photo-generated charges, in other words photovoltaic effect. However, most ferroelectrics show very small conversion efficiency primarily due to their large bandgap and small photocurrent. Band-gap engineered ferroelectrics and multiferroics are therefore exciting classes of PV materials.

Band-gap engineered GFO demonstrates small band gap, ~ 1.75 eV and estimated to reach a theoretical quantum efficiency of ~26 %. Process parameter optimization during synthesis of SMO yields band-gap of the order of ~1.5 eV, close to the ideal value. A possible new PV technology based on low band-gap ferroelectrics and multiferroics are being explored.

P. Swarnakar, ICPCM-2018 at NIT Rourkela, India

(ii) Piezoelectric Energy Harvesting using Flexible Piezoelectric Ceramic-Polymer Composite

Piezoelectrics under mechanical loading produces an electromotive force which can drive a current through an external circuit. However, piezoelectrics, mostly ceramics show poor mechanical properties under cyclic loading. Piezoelectric-polymer composite can be a solution towards piezoelectric energy harvesting. We work using lead based and lead-free ceramic-polymer composite towards designing of energy harvesting systems of commercial interest.

Collaborators: K. Das, IIT Bhubaneswar, S. Mukherjee, CSIR-IMMT Bhubaneswar

S. Das et al. Appl. Surf. Sci. 2018, 428, 356

A. Kumar et al. ICPCM 2018 at NIT Rourkela, India

(a) PMN-PT/PDMS composite film

(b) FESEM image of PMN-PT pellet

(d) Output voltage of PMN-PT/PDMS composite

(e) Output current of PMN-PT/PDMS composite

3. Synthesis of transition metal oxide solid state electrolyte for lithium ion batteries

Liquid electrolytes in Li-ion battery comes with the shortcomings of increased flammability, reduced electrochemical stability, low charge retention, toxicity to name a few. Use of solid electrolytes, which is envisaged to circumvent most of the above, is limited by high ionic conductivities of traditional ionic conductors. A good solid electrolyte should possess:

• Large band gap

• High electrochemical decomposition voltage (> 5.5 V)

• Stability against chemical reaction with both electrodes

• High ionic conductivity (10^-5-10^-3 S/cm)

Further the material should be flexible with small Young’s modulus and Poisson's ratio. Currently we are engaged in designing LTP based solid electrolyte with superior electrical and mechanical properties.

Collaborator: S. Pati, IIT Bhubaneswar

S. Sradhasagar et al. ICPCM 2018 at NIT Rourkela, India

4. Multicomponent Alloy Design

(i ) Fe-Cu-Al-Mn Multicomponent alloy system

High entropy alloys are conceptually new class of alloys with exotic functionalities. However, the their detailed crystallographic structure and atom positions have not been studied in a great extent. Such understanding is crucial towards designing novel alloys with tailored properties and structure. We are looking into this aspect of alloy designing using experimental tools as well first-principles density functional calculations as well as molecular dynamics simulations.

Collaborator: P. S. De, IIT Bhubaneswar

Under review: Roy et al. Materialia 2019