Randomly arranged cation-ordered nanoregions in lead-free relaxor ferroelectric K1/2Bi1/2TiO3: Prediction from first-principles study

First-principles density functional calculations are performed to investigate the lattice dynamics, Infrared reflectivity, and Raman intensity spectra of a lead-free ferroelectric K1/2Bi1/2TiO3 system. In particular, the A-site cation ordering in K1/2Bi1/2TiO3 and its effects on lattice dynamics and the Raman spectrum are explored. The results suggest that the cation ordering at the A-site in K1/2Bi1/2TiO3 significantly influences its Raman spectra. From the analysis of theoretical and experimental Raman spectra, it is suggested that randomly arranged cation ordered nanoregions with different A-site orderings are formed in K1/2Bi1/2TiO3 samples. The random arrangement is favored by entropy contributions to free energy and may explain the lack of observed long-range A-site cation ordering in K1/2Bi1/2TiO3. Further, it is suggested that partial A-site cation ordering may also occur in K1/2Bi1/2TiO3 favored by kinetic factors during sample preparation. The Born effective charges of K and Bi ions at the A-site are computed and found to be significantly disparate, thereby suggesting hetero-polar activity at the A-site in K1/2Bi1/2TiO3. The formation of A-site hetero-polar cation ordered nanoregions and their random or/and partially ordered arrangement in K1/2Bi1/2TiO3 may play an important role in the determination of its relaxor properties apart from the dominant role played by polar nanoregions. The computed Infrared reflectivity and Raman intensity spectra are expected to provide benchmark first-principles results for further analysis of experimental spectra and results

Interface magnetoelectric effect and its sensitivity on interface structures in Fe/AgNbO3 and SrRuO3/AgNbO3 heterostructures: A first-principles investigation

The interface magnetoelectric (ME) effect is promising for novel technological applications as it allows the control of interface magnetization at heterointerfaces by the external electric field. Here in this article, we explore the interface ME effect and its sensitivity on interface atomic structure and bonding in ferromagnetic-ferroelectric oxide hetrostructures within the framework of density functional theory. In particular, we consider Fe/AgNbO3 and SrRuO3/AgNbO3 superlattices with different possible defect-free interfaces. Our results suggest that interface magnetization and thereby interface ME effect can critically depend on interface structure. The interface magnetization is found to depend on atomic bondings which are sensitive to atomic displacements at the interface. This leads to ME coupling due to induced change in the interface magnetization as the electric polarization is reversed in the ferroelectric film. In addition, the contribution to interface ME coupling also comes from the change in exchange-splitting between spin-polarized electrons and consequently change in the interface magnetic moments due to ferroelectric polarization reversal. The change in exchange splitting, in turn, is caused by spin-dependent screening of the bound polarization charges at the interface. In Fe/AgNbO3 system, the interface ME coefficient is found to exhibit opposing trend for Fe|AgO and Fe|NbO2 interfaces. In addition to interface ME effect, the formation of ferroelectric interface domain wall (IDW) in these systems is also explored. The IDW is found to form only in SrRuO3/AgNbO3 system with SrO|NbO2 interface due to oppositely oriented strong dipole moments at the two interfaces. The strong dependence of interface ME effect on interface atomic structure may have implication for its experimental observation in oxide heterostructures. In particular, the interface defects may render the conclusive observation of this phenomenon challenging due to resulting fluctuations in the observed data

Synthesis of Unequally Spaced Linear Micro Strip Rectangular Patch Antenna Array Using Improved Local Search Particle Swarm Optimization

Antenna array systems with low side lobe levels are essential for today wireless communication systems. This paper presents the synthesis of unequally spaced linear rectangular micro strip antenna array with minimum side lobe levels using the novel evolutionary algorithm known as improved local search particle swarm optimization (ILSPSO). ILSPSO is a modified version of particle swarm optimization (PSO), in which Gaussian distribution is used to enhance the local search of the PSO. In this paper, ILPSO is applied to optimize the positions of the micro strip antenna elements to suppress the peak side lobe level (PSLL) along with PSO and differential evolution (DE) algorithms. The steps involved in problem formulation along with design examples illustrating the performance of the ILPSO in minimizing the side lobe levels are demonstrated. A 20 and 32 element linear micro strip rectangular patch antenna (MSRPA) element are considered to show the effectiveness of the proposed method. The optimized micro strip antenna array is simulated using high frequency structure simulator (HFSS). The synthesis results demonstrate that the ILSPSO outperforms PSO and DE in terms of producing lower PSLL and convergence rate. The flexibility and ease of implementation of the ILSPSO algorithm is obvious from this paper, showing the algorithms usefulness in other array synthesis problems

Review on Dissolved Organic Carbon and Particulate Organic Carbon in Marine Environment

Quantification the Dissolved and Particulate organic carbon in marine waters is an essential step towards ecosystem modeling and understanding carbon sequestration processes. A detailed view of estimated and recorded carbon concentration from Arctic to Antarctic is the prime goal of this review. This review compiles some of the important research work carried out in quantifying the organic carbon available in off shore and open waters and in coral reef environment. The cited literatures were collected, grouped and carefully analyzed to give a comprehensive view on current status of marine environment with regard to distribution of dissolved and particulate organic carbon.   Keywords: DOC, POC, continental shelf waters, open sea waters, coral reef environment

Theoretical investigation of surface electronic structure and thermodynamic energies of (1x1) polar and nonpolar K1/2Bi1/2TiO3 (001) surfaces

Theoretical investigations are carried to explore surface electronic structure and surface energetics of (1 × 1) polar and nonpolar (001) surfaces of room temperature tetragonal phase of lead-free relaxor ferroelectric K1/2Bi1/2TiO3 (KBT) within the framework of density functional theory. In particular, polar (KO)-, (BiO)+ and non-polar (TiO2)0 terminations with bulk P4mm symmetry and non-polar (K1/2Bi1/2O)0 and (TiO2)0 terminations with bulk P4bm symmetry are explored. The electronic structures of different terminations differ significantly with respect to bulk and with each other due to surface charge compensation. In case of BiO termination, the Fermi level shifts just above the conduction band minimum (CVM), whereas in case of KO termination, it shifts just below the valence band maximum (VBM) resulting in formation of localized surface states in the band gap with conduction and valence band character. In addition, localized surface states are also formed in the gap at ~11 eV below the VBM. These deep energy localized surface states may be expected to have important implications for surface relaxation and thermodynamic stability of surfaces and their reconstructions. For polar surfaces, surface relaxations are found to be strongly dependent on surface charge and are quite disparate as compared to that for non-polar surfaces. Surface energy of K1/2Bi1/2O termination is found to be much smaller than KO, BiO and TiO2 terminations, suggesting that stacking sequence -K1/2Bi1/2O–TiO2–K1/2Bi1/2O–TiO2- of non-polar planes is significantly favorable energetically than the sequence -KO-TiO2-BiO-TiO2- KO- of polar and non-polar planes in KBT. The preferred stacking sequence of non-polar planes may be expected to have significant influence on the degree of A-site cation ordering in K1/2Bi1/2TiO3

Surface electronic structure, thermodynamic stability of Na1/2Bi1/2TiO3 (001) surfaces and their relevance to A-site cation ordering in bulk phases: A first-principles study

Surface electronic structure and energetics of (001) surfaces of relaxor ferroelectric Na1/2Bi1/2TiO3 (NBT) are explored theoretically within the framework of ab-initio density functional theory. In particular, polar and nonpolar surfaces of tetragonal NBT with bulk P4mm and P4bm symmetries are explored. For P4mm symmetry, (NaO)-, (BiO)+ and (TiO2)0 terminated surfaces and for P4bm symmetry, (Na1/2Bi1/2O)0 and (TiO2)0 -terminated surfaces are considered. The surface electronic structures for different terminations are found to differ with respect to bulk and with each other due to different polarity compensation mechanisms. In case of (BiO)+ and (NaO)- terminated surfaces, the Fermi level shifts slightly above the conduction band minimum (CBM) and below the valence band minimum (VBM) respectively. The resulting localized surface gap states near the VBM and CBM provides sufficient positive and negative charge required for compensation in agreement with the polarity compensation criteria. Furthermore, localized surface states are also formed at energies (~12 eV) deep in the gap below the VBM. The relative thermodynamic stability, reconstructions and relaxations of NBT surfaces may be expected to be correlated with the formation of these deep energy localized surface states. The magnitudes of surface relaxations are found to depend strongly on the nominal charges of the surfaces. The surface energies of polar NaO, BiO and nonpolar TiO2 terminations are found to be significantly larger than that of nonpolar Na1/2Bi1/2O termination. Thus the arrangement of nonpolar-nonpolar planes forming the sequence –Na1/2Bi1/2O–TiO2–Na1/2Bi1/2O–TiO2- may be expected to be more favourable than the sequence of polar-nonpolar planes -NaO-TiO2-BiO-TiO2-NaO-. This favourable arrangement of nonpolar planes may likely influence the degree of A-site cation ordering in Na1/2Bi1/2TiO3 which in turn may influence the degree of coexistence of R3C and CC phases of NBT at the room temperature

Optimum discharge energy density at room temperature in relaxor K_1/2Bi_1/2TiO₃ for green energy harvesting

Lead free polycrystalline K1/2Bi1/2TiO3 (KBT) was prepared by solid state reaction method. Experimentally observed frequencies of Raman modes signified its tetragonal phase and matched reasonably well with theoretically calculated values. The relaxor nature of this material was observed in the temperature dependent real part of permittivity and dielectric loss curve. The value of the degree of diffusiveness was estimated from the modified Curie-Weiss law, which is 1.99, confirmed its relaxor behavior. The validation of this behavior was justified by the Vogel-Fülcher relation. The shoulder in the imaginary part of the modulus (M") and permittivity (Ԑ") spectra revealed the presence of polar nano regions (PNRs). The evidence of PNRs was detectable above freezing temperature which became weaker when the temperature exceeded Tm (temperature at the maximum of dielectric constant). Electric field induced polarization and strain curve showed the stabilization of long range ferroelectric order of the specimen at room temperature. Moreover, we obtained the discharge energy density and strain of 0.46 J/cm3 and 0.12%, respectively, at the maximum application of the electric field of 115 kV/cm at room temperature

An Experimental Study on the Carbon Flux within the Coral Community

The flux of carbon within the coralline ecosystem has been a subject of great interest in the recent decades. So far several studies had been conducted to understand actual process of carbon transfer within this system and it is an elusive factor on science because of the complex process. An attempt had been made to delineate the source and sink of carbon within the coral ecosystem by establishing small experimental set up in the present study.  For these study, four experimental tanks, each consisted of a different community of coral ecosystem was set up in Pondicherry University, Port Blair, Andaman Islands, India. The Tank A was set up with a most prevalent sponge species Stylissa massa, in this part of the study area, Tank B consisted of sponge Lamellodysidea spp., Tank C consisted of macroalgae community i.e. of Padina spp. of an area of 620 cm2 and Tank D had a soft coral Sarcophyton spp. All these species were collected from Burmanallha, a region characterized by rich species diversity. The results indicated that the algal and sponge community provided carbon to support the growth of coral reefs. Coral utilized this carbon for their growth. It was also observed that fluctuation of environmental and physical parameters induced biological stress within the life forms resulted in the release of excess inorganic carbon to the surrounding water. Whenever, the opportunity were available this carbon was utilized by the system itself and managed full extent without any excess carbon