P. S. Ramu Murthy’s research while affiliated with Dhempe College of Arts and Science and other places

This study investigates the consequence of Mn substitution in SrLa1-xMnxLiTeO6 (0 ≤ x ≤ 0.3) perovskites to tune their optical, structural, and dielectric properties for potential optoelectronic applications. The presence of a P21/n monoclinic structure in every composition was determined by analyzing the diffraction patterns at room temperature. The consistency in the peak positions in all the compositions indicates that Mn³⁺ is successfully substituted for La³⁺. Rietveld refinement revealed changes in the unit cell’s volume upon Mn doping. The x = 0 (parent compound) exhibited a double perovskite structure of the ordered type. Variations in the bond angles and lengths are observed across all compositions. Octahedral tilting is observed in all compositions brought about by variations in the tolerance factor ‘t’ and the tilting angle ‘ɸ.’ The FTIR spectra confirm the perovskite structure with characteristic vibrational features indicative of perovskite-type bonding and Mn substitution effects. The 472–488 cm⁻¹ peaks can be attributed to Mn–O and Li–O stretching vibrations, observed peak shifts with increasing x indicating local structure modification, and possible Mn-induced strain in the lattice. Strong absorption bands observed at 662–686 cm⁻¹ correspond to Te–O stretching vibrations within the TeO6 octahedra, confirming the presence of Te in the perovskite structure. UV–visible studies revealed decreased band gap energy from 4.3 eV in the undoped composition to 2.17 eV in the doped composition (x = 0.3) with increasing Mn content, suggesting enhanced conductivity. This also indicates that Mn doping introduces new electronic states within the band gap, thereby reducing the energy for the required electronic transitions. The observed transitions in the UV region, involve d-d transitions within the Mn³⁺ ions combined with the charge transfer from the oxygen ligands to Mn³⁺. Raman spectra recorded for all compositions indicated the symmetry is the same for all compositions and the successful doping of Mn into the parent compound. SEM and EDX analysis verified the elemental composition and highlighted the presence of particle clustering. Impedance spectroscopy analysis indicated a hike in AC conductivity with a hike in frequency and a drop in grain resistance for all compositions, pointing to a single dielectric relaxation mechanism. Cole–Cole plots depicted a non-Debye-type behavior, attributed to inherent defects within the materials. Dielectric studies demonstrated a frequency-dependent drop in both dielectric constant and tangent loss, suggesting a reduction in net polarization at higher frequencies. Hence, the work carried out here addresses the lack of detailed understanding of how Mn doping affects the structural, optical, and dielectric properties of SrLaLiTeO6, a material with the potential for photovoltaic and optoelectronic applications, and specifically explores the impact of Mn doping bandgap reduction and dielectric enhancements, which are vital for improving material performance in applications like semiconductors and LEDs.

We prepared bulk samples of SrLaLiTe1-xGdxO6; 0 ≤ x ≤ 0.3, using the solid-state method. Measurements carried out on the XRD data recorded at room temperature highlighted changes corresponding to the volume of the unit cell and angle β. Specifically, the undoped composition described a structure of the ordered type containing Li⁺ and Te⁶⁺. Calculations of the octahedral tilt angle indicated a transition from cubic to monoclinic symmetry, accompanied by bending and tilting of the B-O-B’(B = La, B’ = Te/Gd) octahedra. FTIR measurements confirmed the existence of molecular bonds in all compositions. UV–visible spectroscopy results indicated a reduced bandgap energy, suggesting enhanced conductivity in the doped samples. SEM and EDX confirmed the elemental composition and revealed particle clustering. Impedance spectroscopy analysis demonstrated increased AC conductivity at higher frequencies. Additionally, a decrease in the grain resistance indicated single dielectric relaxation behavior. A relaxation phenomenon of the non-Debye type was revealed from the Cole–Cole plots attributed to the presence of imperfections within the samples. Dielectric properties showed a reduction in dielectric loss and constant, which was dependent on frequency, attributed to the decrease in overall polarization.

SrLaLiTe1-xZnxO6; x = 0,0.1,0.2,0.3 were investigated for their structural, optical and dielectric properties. The compositions were found to be monoclinic with the P21/n space group. Rietveld refinement of the X-ray data revealed a change in the cell volume and monoclinic cell angle β. The x = 0 composition exhibited the ordered double perovskite structure SrLaLiTeO6 with Li+ and Te6+.Tolerance factor and tilting angle calculations indicated a change in symmetry due to tilt of the octahedra and bending of Li–O–Te/Zn. FTIR studies confirmed that molecular bonds are present in the double perovskite structure. UV–visible reflectance measurements revealed a drop in the band gap energy indicating that the doped compositions have a better ability to conduct. SEM and EDX studies showed all compositions having an almost uniform distribution in terms of their shape, particles were grouped together, and confirmation of the element composition. Impedance spectroscopy studies indicated that the AC conductivity increases as the frequency increases. Single dielectric relaxation is also seen to be present in all compositions due to a decline in the grain resistance Rg. Cole–Cole plots revealed a non-Debye type of relaxation phenomena due to imperfections in all compositions. Dielectric studies indicated a decrease in the dielectric constant and loss with increasing frequency due to a drop in net polarization.

Li and Te doping at the B and B’ sites of SrLaLi1-xTe1+xO6 and its effect on the structure and band gap were investigated for the first time for −0.2 ≤ x ≤ 0.2. All the samples were found to be crystallized in the monoclinic structure with space group P21/n thereby suggesting the formation of a double perovskite. The cell volume is seen to vary almost linearly for all compositions authenticating the formation of single-phase. A deviation from pseudo-cubic symmetry is observed from Li rich to Te rich compositions in terms of the monoclinic cell angle. A linear variation in the tolerance factor suggests that the doping of Te for Li permits for a better matching of the Sr/La-O and Li/Te-O bond distances as compared to Li for Te doping. Optical band gap measurements indicate a reduction in the width of the conduction band causing a rise in the energy Eg.