We investigate the unusual phase transitions in SrRuO3 and 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 and Tc in 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.

We investigate room temperature core level and valence band spectra of BaBiO 3 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 ). 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 p 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.

In this work, we have investigated the precursor effects to superconductivity in BaPb0.75Bi0.25O3 using 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. above TC, our results show an increase in both the orthorhombic and tetragonal strain. The well screened features observed in Bi and Pb 4f7/2 core 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.closing of the band gap at the Fermi level.

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 as prepared 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 as prepared 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.

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