Synthesis, Structural and Dielectric Studies on SrBi2-xGdxNb2O9 Lead Free Ceramics

In this manuscript, the structural and dielectric properties of Gadolinium (Gd3+) substituted at Bi-site of SrBi2-xGdxNb2O9 (x= 0.0, 0.4, 0.6 and 0.8) prepared by using solid state reaction are studied. XRD analysis revealed the formation of single phase with orthorhombic structure in SBN and Gadolinium modified SBN. It is found that cell parameters and volume were decreased with increase of Gd3+ ion concentration in SBN. SEM analysis revealed that the samples possess well defined needle shaped grains. The grain size of SBN was hindered by the presence of Gd3+ ion at Bi-site. The growth of single phase layered perovskite structure was confirmed from FTIR and Raman spectroscopy. The dielectric properties of Gd3+ ion doped SBN ceramics are studied as a function of frequency (50Hz-1MHz) from room temperature to 500ºC. It is observed that phase transition temperature (Tc) decreased from 430ºC to 330ºC with increase of frequency due to incorporation of Gd3+ ion in SBN. The broadness of peaks and decrease in Tc indicate the transition from a normal ferroelectric to ferroelectric-relaxor type. The study on variation of tanδ with temperature at different frequencies indicates that tanδ has larger values at higher temperatures. Further, the diffuseness parameter (γ) has been computed for all the compositions.

Ultra-high energy storage performances regulated by depletion region engineering sensitive to the electric field in PNP-type relaxor ferroelectric heterostructural films

PNP-type heterostructured films of P-type Na0.5Bi3.25La1.25Ti4O15 and N-type BaBi3.4Pr0.6Ti4O15 layers with the same Aurivillius layered perovskite structure are designed to regulate the energy storage performances by depletion region engineering.

Single-phase multiferroics: new materials, phenomena, and physics

Multiferroics, where multiple ferroic orders coexist and are intimately coupled, promise novel applications in conceptually new devices on one hand, and on the other hand provide fascinating physics that is distinctly different from the physics of high-TC superconductors and colossal magnetoresistance manganites. In this mini-review, we highlight the recent progress of single-phase multiferroics in the exploration of new materials, efficient roadmaps for functionality enhancement, new phenomena beyond magnetoelectric coupling, and underlying novel physics. In the meantime, a slightly more detailed description is given of several multiferroics with ferrimagnetic orders and double-layered perovskite structure and also of recently emerging 2D multiferroics. Some emergent phenomena such as topological vortex domain structure, non-reciprocal response, and hybrid mechanisms for multiferroicity engineering and magnetoelectric coupling in various types of multiferroics will be briefly reviewed.

Superconductivity in a unique type of copper oxide

The mechanism of superconductivity in cuprates remains one of the big challenges of condensed matter physics. High-Tc cuprates crystallize into a layered perovskite structure featuring copper oxygen octahedral coordination. Due to the Jahn Teller effect in combination with the strong static Coulomb interaction, the octahedra in high-Tc cuprates are elongated along the c axis, leading to a 3dx2-y2 orbital at the top of the band structure wherein the doped holes reside. This scenario gives rise to 2D characteristics in high-Tc cuprates that favor d-wave pairing symmetry. Here, we report superconductivity in a cuprate Ba2CuO4-y, wherein the local octahedron is in a very exceptional compressed version. The Ba2CuO4-y compound was synthesized at high pressure at high temperatures and shows bulk superconductivity with critical temperature (Tc) above 70 K at ambient conditions. This superconducting transition temperature is more than 30 K higher than the Tc for the isostructural counterparts based on classical La2CuO4. X-ray absorption measurements indicate the heavily doped nature of the Ba2CuO4-y superconductor. In compressed octahedron, the 3d3z2-r2 orbital will be lifted above the 3dx2-y2 orbital, leading to significant 3D nature in addition to the conventional 3dx2-y2 orbital. This work sheds important light on advancing our comprehensive understanding of the superconducting mechanism of high Tc in cuprate materials.