BaTiO3-Based Lead-Free Electroceramics with Their Ferroelectric and Piezoelectric Properties Tuned by Ca2+, Sn4+ and Zr4+ Substitution Useful for Electrostrictive Device Application

Dense microstructure BaTiO₃ (BT) ceramic with c/a ~1.0144 and average grain size ~7.8 μmis developed by achieving the ferroelectric parameters Psat. = 24.13 μC/cm2 and Pr = 10.42 μC/cm2 with lower coercive field of Ec = 2.047 kV/cm. For BT ceramic, the “sprout” shape nature is observed for strain-electric field measurements with remnant strain ~ 0.212%, converse piezoelectric constant ~376.35 pm/V and electrostrictive coefficient Q33~ 0.03493 m4/C2. To tune the piezoelectric properties of BT ceramic, the substitutions of Ca2+ and Sn4+, Zr4+ are done for Ba2+ and Ti4+ sites respectively. The Ba0.7Ca0.3Ti1-xSnxO3 (x = 0.00, 0.025, 0.050, 0.075, and 0.1, BCST) system was studied with ferroelectric, piezoelectric and electrostrictive properties. The electrostrictive coefficient (Q33) ~ 0.0667 m4/C2 was observed for x = 0.075 and it is higher than the lead-based electrostrictive materials. Another (1-X) Ba0.95Ca0.05Ti0.92Sn0.08O3 (BCST) – (X) Ba0.95Ca0.05Ti0.92Zr0.08O3 (BCZT), ceramics (x = 0.00, 0.25, 0.50, 0.75, and 1) is studied. The BCST-BCZT ceramic system shows the increase of polymorphic phase transition temperatures toward the room temperature by Ca2+, Sn4+ and Zr4+ substitution. For BCST-BCZT system the composition x = 0.75 exhibits the d33, and Q33 values of 310 pC/N, 385 pm/V and 0.089 m4/C2 respectively which is greater than BT ceramics

The idea of a new Zimbabwe post- Mugabe

Zimbabwe has gone through deep political, economic and social challenges for close to three decades. Once known as the shining light of Africa, Zimbabwe is now often known for dominating international headlines for the wrong reasons. In November 2017, the country experienced a radical change to the constitutional and political order, which brought an end to former President Robert Mugabe’s 37-year reign. Emmerson Mnangagwa, who was once Mugabe’s right-hand man, assumed leadership of both the country and the ruling Zimbabwe African National Union–Patriotic Front (ZANU–PF). He was reelected in the July 2018 harmonised elections, although under disputed circumstances. The removal of Robert Mugabe has provided the country an opportunity to break from the past, and hopes have been raised for the birth of a new Zimbabwe. This chapter explores some of the measures that the administration post-Mugabe should implement to set the country on a new path. Thus, the purpose of this chapter is not to argue for a particular political formation or political leaders to govern. Rather, its objective is to explore whether the idea of a new Zimbabwe is possible and what it would take to realise this objective. Before discussing the prospects for this desired state of affairs, it is important to examine the current situation, which is explored in the first part of the chapter. A brief overview of the fall of Mugabe and rise of Mnangagwa is then provided to show how a leader who commanded respect beyond the shores of our continent could exit in such an undignified manner. The core section is dedicated to a discussion of the prospects for a new Zimbabwe, and concluding remarks end the chapter

Population dynamics and genetic connectivity in recent chimpanzee history

Knowledge on the population history of endangered species is critical for conservation, but whole-genome data on chimpanzees (<Pan troglodytes) is geographically sparse. Here, we produced the first non-invasive geolocalized catalog of genomic diversity by capturing chromosome 21 from 828 non-invasive samples collected at 48 sampling sites across Africa. The four recognized subspecies show clear genetic differentiation correlating with known barriers, while previously undescribed genetic exchange suggests that these have been permeable on a local scale. We obtained a detailed reconstruction of population stratification and fine-scale patterns of isolation, migration, and connectivity, including a comprehensive picture of admixture with bonobos (Pan paniscus). Unlike humans, chimpanzees did not experience extended episodes of long-distance migrations, which might have limited cultural transmission. Finally, based on local rare variation, we implement a fine-grained geolocalization approach demonstrating improved precision in determining the origin of confiscated chimpanzees

Structure composition correlation in KNN-BT ceramics - An X-ray diffraction and Raman spectroscopic investigation

Lead free (1 - x)K0.5Na0.5NbO3-(x)BaTiO3 ceramics were synthesized by solid state reaction. The influence of the addition of BaTiO3 on the phase and crystalline symmetry of the KNN-based ceramics was investigated. X-ray analysis confirmed that the addition of BaTiO3 results in the change of structure from orthorhombic towards tetragonal at x = 0.04 and cubic phase above x = 0.1. The tetragonality ratio increased from 1.005 at x = 0.04 to 1.022 at x = 0.08 and then decreased. Raman spectra demonstrated a variety of changes with BT addition, mainly classified as lattice translations involving motions of the alkaline cations and internal modes of NbO6 octahedra. The symmetric stretching mode nu(1) shifted to a higher wavenumber as the concentration of BT is increased, because the incorporation of BaTiO3 in the perovskite unit distorted the O-Nb-O bond angles. A linear relationship was observed in tetragonality ratio calculated by XRD and Raman shifts. This correlation between XRD and Raman spectroscopy results can be used to assess the crystalline symmetry in KNN-modified systems. (C) 2013 Elsevier B.V. All rights reserved

Synthesis and microwave dielectric behavior of (Bi1−xPbx)NbO4 ceramics

Ceramic samples of (Bi1−xPbx)NbO4 (x=0, 0.025, 0.05, 0.10, 0.15, 0.20) with 0.75wt.% V2O5 addition sintered at 920∘C, 940∘C and 960∘C are investigated. Pb is selected as a substitute for Bi3+ in BiNbO4 ceramics as it exists in two stable valence states of +2 and +4 and the average valency matches to that of Bi3+. The average Shannon radius (for octahedral coordination) of Pb2+ (1.19Å) and Pb4+(0.775Å) cations is 0.9825Å, which is similar to that of Bi3+ ion (1.03Å). The dense (>94%) polycrystalline (Bi1−xPbx)NbO4 samples fabricated mostly reveal orthorhombic (Pnna) phase (α-BiNbO4, Sp. Gp. 52) by powder XRD. Presence of satellite Pb2Nb2O7 phase, the amount of which is increasing with increase in Pb content, is also noticed. The microwave dielectric constant (εr′) values of the niobates are found to increase from 42 to 71, whereas the quality factor (Qu.f) values are found to decrease from 5400 to 550 GHz with increasing substitution of Pb. The compositions so synthesized are important as hardly there are any microwave dielectric ceramics available with 45<εr′<75