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

Enhancement of magnetic and electrical properties in Sc substituted BiFeO3 multiferroic

Polycrystalline BiFe1-xScxO3 (x=0, 0.05, 0.1 and 0.15) compounds are prepared using solid state reaction. The XRD patterns show that all compounds are crystallized in rhombohedral structure with R3c space group. An induced weak ferromagnetism in Sc substituted BiFeO 3 due to suppression of spiral modulated spin structure is revealed. In addition, a spin glass like behaviour is observed from the zero field cooled (ZFC) and field cooled (FC) magnetization curves in the low temperature region. Further, the coupling between the ferroelectric and (anti) ferromagnetic orders is evident from the appearance of anomaly in the dielectric data near the magnetic Néel temperature (373 °C). The reduction of oxygen vacancies due to Sc substitution is evident from the ac conductivity data and the suppressed anomaly in dielectric data at 220 °C. The temperature dependence of ac conductivity is consistent with correlated barrier hopping (CBH) model. The temperature dependent ac conductivity and activation energies indicate that electronic conduction, oxygen vacancies movement and creation of defects are the prime contributors to the ac conductivity in measured temperature regions. The improved magnetic and electrical properties due to the structural modification are prominent for novel device applications

Dielectric Studies of Agta0.5Nb0.5O3

The complex perovskite oxide AgNb0.5Ta0.5O3 (ATN) synthesized by solid state reaction techinique has single phase with monoclinic structure.The scanning electron micro graph of the sample shows that grains and grain boundary are there but grain size is not definable from there. The field dependence dielectric response and loss tangent were measured in the temperature range from 30o C to 430 o C and in the frequency range from 100Hz to 1MHz. An analysis of the dielectric constant (ϵ’) and loss tangent (ta

Theoretical and experimental investigation of Raman modes, ferroelectric and dielectric properties of relaxor Na0.5Bi0.5TiO3

We use a combination of first-principles density functional theoretical analysis and experimental characterization to understand the lattice dynamics, dielectric and ferroelectric properties of lead-free relaxor ferroelectric Na0.5Bi0.5TiO3 (NBT) system. Vibrational spectrum determined through our calculations agrees well with the observed Raman spectrum, and allows assignment of symmetry labels to modes. The calculated Born effective charges reveal (a) two distinct types of Ti ions at the B-site with anomalous dynamical charges differing by up 1.6e, and (b) Na and Bi ions at the A-site exhibit disparate dynamical charges of about 1 and 5.5e, respectively. Thus, there exist hetero-polar activity at both A and B-sites in NBT, and disorder associated with these hetero-polar ions is responsible for its relaxor behaviour. Large dielectric response of NBT arises primarily from phonons, and specifically the modes involving Bi-O (109 cm-1) and Ti-O (246, 276 cm-1) vibrations, respectively

Synthesis And Characterization of ferroelectric material (Na0.5Bi0.5)TiO3- Eu2O3

Lead free Na0.5Bi(0.5-x)EuxTiO3 ceramics were prepared by solid state reaction route taking five different composition with x=0.005,0.01,0.02,0.03,0.04 and 0.05 . From XRD pattern it is comfirmed that theNBT-Eu single phase were formed at differnt Eu2O3 doping. RAMAN pattern shows roughness or irregularity due to the data taken at high resolution . From morphological study by SEM it is found that the grains were well developed and have the dense structure. Also the grain shape changes from granular to plated with increase in concentreation of Eu2O3. From UV-VIS SPECTROSCOPY it is observed that the band gap increase with increase Eu2O3 concentration. The PE-LOOP analysis shows that the remnant polarization (Pr) and coercive field (Ec) values increase with increase in concentration. The dielectric constant increases with increase in tempreature also the broadening of the peaks is observed with increase in concentration

Molecular characterization of MHC-DRB cDNA in water buffalo (Bubalus bubalis)

In the present study, water buffalo MHC (Bubu)-DRB cDNA was cloned and characterized. The 1022 base long-amplified cDNA product encompassed a single open reading frame of 801 bases that coded for 266 amino acids. The Bubu-DRB sequence showed maximum homology with the BoLA-DRB3*0101 allele of cattle. A total of seven amino acid residues were found to be unique for the Bubu-DRB sequence. The majority of amino acid substitutions was observed in the β1 domain. Residues associated with important functions were mostly conserved. Water buffalo DRB was phylogenetically closer to goat DRB*A

Evaluation of Physiological Parameters in Response to Endurance Exercise of Zanskar Ponies Adapted to High Altitude of Ladakh Region

Zanskar pony, a native horse breed of Ladakh mainly used for transportation in Trans-Himalayan region of India, is well adapted to high altitude hypobaric hypoxia environment. Due to extreme conditions of the Ladakh region, better endurance of these ponies under hypoxic and extreme cold conditions is of utmost concern for their recruitment in Indian Army. In the present study, 12 young trained Zanskar ponies were evaluated during endurance exercise at an altitude of 3292 meter above mean sea level. The animals were subjected to carriage transport with 65-70Kg load or riding on a track of 5-6 Km. Physiological parameters viz., pulse rate (PR), heart rate (HR), rectal temperature (RT), respiratory rate (RR) and oxygen saturation (SaO2) were recorded in Zanskar ponies during pre-exercise (T0), post- exercise (T1) and post recovery (T2, 2 hours post resting) stages. Results showed marked increase in PR, HR, RR and RT post exercise time points. The mean values of PR increased from 49.83±4.62 to 73.67±21.54 per minute, HR from 48±13.60 to 75±15.82 beats/min, RR from 37.83±9.70 to 57.67±13.48 per min and RT from 99.62±0.34 101.04±0.53 °F from pre stress to post endurance stress. The mean SaO2 level reduced significantly (88.58±6.75 at T0 versus 64.00±18.70 at T1 and 54.42±14.79 at T2) post exercise. This indicated limited availability of arterial oxygen for tissues which could be vital factor for adverse change in some of physio-biochemical parameters. Though the trend of physiological response was similar for all the 12 animals, still variation at individual animal level was observed during endurance stress. In future, some of these physiological parameters along with biochemical and molecular parameters could be evaluated as potential biomarkers in selecting ponies with superior endurance trait specifically under hypoxic conditions

Sequence Characterisation and Genotyping of Allelic Variants of Beta Casein Gene Establishes Native Cattle of Ladakh to be a Natural Resource for A2 Milk

Bovine milk is regarded as nature's perfect food due to presence of vital nutrients. However some peptides are generated after proteolytic digestion of β-casein that have opioid properties and may increase the risk of chronic diseases. There are 13 genetic variants of bovine beta-casein; out of these A1 and A2 are the most common in dairy cattle breeds. The A1 and A2 variants differ only at position 67, which is histidine in A1 or proline in A2 milk. Earlier published reports have indicated that A1 β casein could be responsible for several health disorders like diabetes, coronary heart disease etc. while A2 β-casein is generally considered safe for human consumption. In the present study, an effort was made to sequence characterize β casein gene and identify allelic distribution of A1A2 alleles in native cattle of Ladakh region adapted to high altitude and low oxygen condition. The data showed 2 non-synonymous variations in coding region, while 5’UTR was completely conserved. The 3’UTR showed 2 more variations in Ladakhi samples. Further, the genotyping in 85 Ladakhi cattle for A1A2 alleles revealed that in Ladakhi cattle, A2 allele is predominantly present as reported for some of the other Indian breeds. The frequency of A2 allele was 0.90 and frequency of A2A2 genotype was found to be 0.79 in Ladakhi cattle. The present data strongly indicate that local cattle of Ladakh with higher frequency of A2 allele and A2A2 genotype is natural resource for A2 milk.  Systematic efforts should be made for long term conservation and genetic improvement of this invaluable genetic resource of Ladakh

First principles study of lead free piezoelectric AgNbO 3 and (Ag 1-xK x)NbO 3 solid solutions

We present an ab-initio study of structural, electronic and ferroic properties of lead-free orthorhombic AgNbO 3 in centrosymmetric Pbcm and recently proposed noncentrosymmetric Pmc2 1 space group symmetries. The calculated polarization of AgNbO 3 in Pmc2 1 phase is ∼0.09 μC/cm 2, whereas it is 55.9 μC/cm 2 in the ideal cubic phase. The large polarization of AgNbO 3 in the ideal cubic structure is attributed to off-centering of Ag as well as Nb ions at the A and B sites, respectively. In our calculations both phases (Pmc2 1 and Pbcm) of AgNbO 3 show small relative energy difference (∼0.1 meV/f.u), thus suggesting the coexistence of centrosymmetric and non-centrosymmetric phases and thereby antiferroelectric and ferroelctric order in room temperature AgNbO 3 polycrystals. We further study structural properties and spontaneous polarization in orthorhombic Pmc2 1 Ag 1-xK xNbO 3 solid solutions. The calculated spontaneous polarization of AgNbO 3 is enhanced due to suppression of NbO 6 octahedral tilt angles as K ion is substituted at Ag sites. Our study suggests that appropriate cation substitution should indeed result in the improvement of ferroelectric properties of lead-free AgNbO

The structural and electronic properties of cubic AgMO3 (M=Nb, Ta) by first principles calculations

We report the electronic structure of the AgMO3(M=Nb, Ta) within the frame work of density functional theory and calculations are performed within the generalized gradient approximation (GGA) by using ultrasoft pseudopotentials. The calculated equilibrium lattice parameters and volumes are extracted from fitting of Birch third order equation of state and which are reasonable agreement with the available experimental results. The density of states,band structure of Ag(Nb,Ta)O3 reveals that the valance bands mostly occupied with O-2p and O-2s states and whereas conduction band occupied with Nb (Ta) 4d(5d) states including less contribution from Ag 5s states