Investigation of magnetic exchange interactions in Cr-dopedCa0.5Sr0.5RuO3.

The value of Curie temperature (TC) and resistivity forCa0.5Sr0.5Ru1-xCrxO3are found to increase with increase inxfrom 0 to 0.1. TheTCincreases from 38 K to 107 K. In this work, we investigate the increment using spin polarised density functional theory. The compounds exhibit Griffiths phase. Our results show that to understand the behaviour of the increase inTC, it is important to consider not only the competing super exchange and super-super exchange interactions between Ru/Cr-Ru/Cr ion pairs but also the increment in the value of the magnetic moment due to the localized character of the dopant (Cr) ion. Our results suggest that the increased resistivity with Cr doping could be due to increased scattering rate and strong on-site coulomb repulsion due to Cr doping. It is also important to note that the behaviour ofTCwith the Ru-O-Ru bond angle is not in line with the functional form reported for ferrites, chromites and some ferromagnetic oxides. We believe that our results will be helpful in further exploring the origin of magnetism and transport on Cr doping in perovskite ruthenates.

Structural and physical properties of Ni1-xVxalloys around and away from quantum critical point.

We investigate the room temperature structure (global and local), temperature dependent magnetic and transport behaviour of Ni1-xVx(0⩽x⩽0.13) alloys. Our Energy Dispersive Analysis of x-rays results show that the prepared compositions are stoichiometric. With increase in V doping, the compounds exhibit a quantum phase transition aroundxc= 0.12, where the ferromagnetic phase is suppressed. Our results show that all the compounds stabilize in face centred cubic structure at RT and the lattice parameter shows unusual behaviour close toxc. The magnetic and heat capacity studies show signature of Griffiths phase on either side ofxc. From 25 K to the lowest collected temperature, we observe a linear T dependence of resistivity atx = 0.1 and aroundxc, which is separated by a Fermi-liquid region aroundx = 0.106. This suggests that the origin of the transport behaviour is different around the quantum critical point and away from it. Our Ni K-edge x-ray Absorption Spectroscopy results show that there is a significant reduction in the first coordination number around Ni central atom on doping. Further, with doping, there is distortion in the first coordination shell around Ni. This suggests, with V doping, the local structure around Ni is different from the global structure as obtained from the x-ray Diffraction results. Interestingly, with doping, we observe a direct connection between the extent of distortion at RT and the magnetic disorder obtained at 2 K. We believe our results will motivate the scientific community to further study the interplay between the structural disorder and quantum fluctuations with temperature at the local level.

Pseudogap in BaPbxBi1‒xO3(x = 0.7, 0.75 and 1.0).

In this work, we have investigated the crystal and electronic structure of the orthorhombic phase of BaPbxBi1-xO3(BPBO) forx = 0.7 (BPBO70), 0.75 (BPBO75) and 1.0 (BPO), using temperature dependent x-ray diffraction measurements, photoemission spectroscopy, and electronic structure calculations. Our results show the importance of particle size and strain in governing superconductivity. Interestingly, the temperature evolution of the structural parameters in the case of BPBO70 is similar to that of BPBO75 but the magnitude of the change is diminished. The BPBO75 and BPO compounds exhibit metallic nature, which is corroborated by the core level studies. The electronic structure calculations in conjunction with the core level studies suggest that oxygen vacancies play an important role for metallicity observed in the end compound. The exponent to the spectral line shape close to the Fermi level suggests the origin of pseudogap to be due to other contributions in addition to disorder in the case of BPBO70 and BPO. The core level studies also show that as one goes fromx = 0.70 to 1.0, there occurs chemical potential shift towards the valence band suggesting hole doping. Our results open the venue to further study these compounds as a function of particle size, nature of carriers for its transport behaviour, electronic structure belowTC, composition at the grain boundaries and microscopic origin of pseudogap in the non-superconducting phase. We believe that our results call for a revision of the temperature-doping phase diagram of BPBO to include the pseudogap phase.

Lattice effects on the physical properties of half-doped perovskite ruthenates.

We investigate the unusual phase transitions in SrRuO3and Sr0.5Ca0.5Ru1-xCrxO3(x = 0, 0.05 and 0.1) employing x-ray diffraction, resistivity, magnetic studies and x-ray photoemission spectroscopy. Our results show the compounds undergo a crossover from itinerant ferromagnetism to localized ferromagnetism. The combined studies suggest Ru and Cr be in the 4+ valence state. A Griffith phase and an enhancement in Curie temperature (Tc) from 38 K to 107 K are observed with Cr doping. A shift in the chemical potential towards the valence band is observed with Cr doping. In the metallic samples, interestingly, a direct link between the resistivity and orthorhombic strain is observed. We also observe a connection between orthorhombic strain andTcin all the samples. Detailed studies in this direction will be helpful to choose suitable substrate materials for thin-film/device fabrication and hence manoeuvre its properties. In the non-metallic samples, the resistivity is mainly governed due to disorder, electron-electron correlation effects and a reduction in the number of electrons at the Fermi level. The value of the resistivity for the 5% Cr doped sample suggests semi-metallic behaviour. Understanding its nature in detail using electron spectroscopic techniques could unravel the possibility of its utility in high-mobility transistors at room temperature and its combined property with ferromagnetism will be helpful in making spintronic devices.

Evidence of lattice strain as a precursor to superconductivity in BaPb0.75Bi0.25O3.

In this work, we have investigated the precursor effects to superconductivity in BaPb0.75Bi0.25O3using temperature dependent resistivity, x-ray diffraction technique and photoemission spectroscopy. The present compound exhibits superconductivity around 11 K (TC). The synthesis procedure adopted is much simpler as compared to the procedure available in the literature. In the temperature range (10 K-25 K) i.e. aboveTC, our results show an increase in both the orthorhombic and tetragonal strain. The well screened features observed in Bi and Pb 4f7/2core levels are indicative of the metallic nature of the sample. The compound exhibits finite intensity at the Fermi level at 300 K and this intensity decreases with decrease in temperature and develops into a pseudogap; the energy dependence of the spectral density of states suggests disordered metallic state. Furthermore, our band structure calculations reveal that the structural transition upon Pb doping results in the closing of the band gap at the Fermi level.

Structural and electronic effects in GdCu alloy.

We have studied structural and electronic phenomena in GdCu using x-ray diffraction (xrd), photoemission spectroscopic (PES) techniques and band structure calculations. Our structural studies show that the as prepared GdCu sample does not stabilise completely in cubic CsCl phase even at room temperature (RT). The thermal hysteresis is observed in the lattice parameter that appears to be due to strain and dislocations at the surface. The behaviour of the intensity of the most intense xrd peak suggests phase coexistence and structural link with magnetic properties. After undergoing thermal cycling to RT, with an increase in polishing depth, the GdCu sample shows different surface and bulk crystal structures at RT. This behaviour is in contrast to the behaviour of the asprepared one. The surface is predominantly cubic while the bulk exposes more its hidden orthorhombic FeB phase with an increase in the depth of polishing. To understand the manifestation of phase separation on the electronic structure, we have used DFT and DFT + U calculations and PES studies. Our results show the importance of on-site Coulombic interaction in Gd 4f and Cu 3d orbitals. At the Fermi edge, in addition to the significant contribution of Gd 5d and Cu 3d, there is also a contribution of Cu 4p states. The PES studies exhibit chemical potential shift as one compares the asprepared GdCu and the GdCu that has undergone thermal cycling. We have discussed the effect of the chemical potential shift on the valence band and core- level spectra. We believe our results will be helpful in providing insight into the generic property displayed by systems that exhibit strain dominated phase separation.

Interplay of lattice distortion and electronic structure in BaBiO3.

We investigate room temperature core level and valence band spectra of BaBiO3 using x-ray photoemission spectroscopy and band structure calculations. The features in the valence band spectrum were studied using density functional theory (DFT) under local density approximation (LDA) and Tran Blaha modified Becke Johnson (TB mBJ) exchange potential. The calculations were performed for three different structural parameters; monoclinic, cubic and monoclinic (M[Formula: see text]). Our results of the core level spectrum and DFT calculations rule out charge disproportionation of the Bi ions. The valence band spectrum displays gap at the Fermi edge and fine structures in the region close to the Fermi edge. The DFT calculation under TB mBJ for the monoclinic structure is able to generate gap and match the energy positions of the fine structure in a better way. Our calculation results show that there are holes in the O 2[Formula: see text] states and unequal transfer of electrons to the states of the Bi ions. Such mechanism could lead to bond disproportionation and its association with the fine structures in the valence band. The current results reveal the significance of strong link between the lattice distortion and electronic structure and hence to its physical properties.

Clinical Evaluation of Root Resorption and its Correlation with Obturation Quality in Pulpectomized Deciduous Teeth with Different Obturating Materials: An In vivo Study.

AIMS AND OBJECTIVES: The aim was to evaluate the root resorption in pulpectomized deciduous teeth and its correlation with obturation quality using zinc oxide and eugenol (ZOE), Metapex and Endoflas at the interval of 6 and 12 months. MATERIALS AND METHODS: A total of 150 infected primary mandibular molars were randomly and equally divided into three subgroups (n = 50 each): Group 1 (ZoE), Group 2 (Metapex), and Group 3 (Endoflas) based on the obturation material preferred. The teeth were clinically and radiographically evaluated at 6 and 12 months' postoperatively by another investigator who was blinded to the type of filling material that was used in each tooth. Kruskal-Wallis test, Mann-Whitney Test, and Wilcoxon Signed-Rank Test was used for statistical analysis. RESULTS: When the obturation quality was assessed, the optimal filling was found in 78% of the cases while the rest have underfilling (9%) and overfilling (13%). The incidence of overfilling was higher in the cases with some root resorption. After 12 months, Group 2 showed maximum variation with the highest incidence (70%) of extensive resorption both interradicular and intraradicular (Grade 3 score) followed by Group 1 (26%) and Group 3 (16%), respectively. CONCLUSION: Among all the materials, Endoflas showed the highest success rate with least incidence of resorption both outside and within the root canal (hollow tube effect) whereas least success rate was observed with Metapex having the hollow tube effect in majority of the cases (70%) after the follow-up of 12 months.