Structural, magnetic, magnetocaloric and specific heat investigations on Mn doped PrCrO3 orthochromites

We have synthesized PrCr0.85Mn0.15O3 (PCMO) chromite and investigated the influence of manganese (Mn) doping at Cr-sites on the structural, magnetic, magnetocaloric and thermal properties of PrCrO3 compound. No structural transition was observed with Mn substitution and the doped compound crystallized into distorted orthorhombic structure with Pnma space group which was confirmed by Rietveld refinement of x-ray powder diffraction patterns. Neel temperature, noticed at 168 K from the temperature variation of magnetization, smaller than that reported for PrCrO3, indicated the influence of Mn3+ substitution in decreasing the antiferromagnetic ordering. Magnetization was almost eight times higher than that reported for undoped sample. Magnetocaloric effect measured via the magnetic entropy change and relative cooling power demonstrated significant values in the temperature range 10-20 K. The values of magnetic entropy change are much superior to that reported for other polycrystalline orthochromites and even at smaller applied field strength. The material exhibited second order magnetic phase transition. The Debye temperature and the density of states at Fermi level were also calculated. The overall results make PrCr0.85Mn0.15O3 chromite a potential candidate to replace the existing materials for low temperature magnetic refrigeration. © 2017 IOP Publishing Ltd

Domain structures and local switching in lead-free piezoceramics Ba0.85Ca0.15Ti0.90Zr0.10O3

Lead-free piezoelectrics are becoming increasingly important in view of environmental problems of currently used lead-based perovskites such as lead zirconate titanate (PZT). One of the recent candidates for PZT replacement, solid solutions of BaZr0.2Ti0.8O3 and Ba0.7Ca0.3TiO3, are investigated in this work by piezoresponse force microscopy. Coexistence of the tetragonal and rhombohedral phases in this material is observed, which probably gives rise to easy polarization switching due to multiple domain states. The period of observed domain lamella scales with the grain size obeying well-known square root dependence characteristic of BaTiO3 ceramics. Domain switching and relaxation are investigated at the nanoscale as a function of the applied voltage and duration of the applied voltage pulses. The observed distortion of piezoresponse hysteresis loops near grain boundaries is attested to the increased concentration of defects. Nanoscale piezoelectric properties of these materials are discussed

Environmentalism in the EU-28 context: the impact of governance quality on environmental energy efficiency

Environmental policies are a significant cornerstone of a developed economy, but the question that arises is whether such policies lead to a sustainable growth path. It is clear that the energy sector plays a pivotal role in environmental policies, and although the current literature has focused on examining the link between energy consumption and economic growth through an abundance of studies, it does not explicitly consider the role of institutional or governance quality variables in the process. Both globalization and democracy are important drivers of sustainability, while environmentalism is essential for the objective of gaining a “better world.” Governance quality is expected to be the key, not only for economic purposes but also for the efficiency of environmental policies. To that end, the analysis in this paper explores the link between governance quality and energy efficiency for the EU-28 countries, spanning the period 1995 to 2014. The findings document that there is a nexus between energy efficiency and income they move together: the most efficient countries are in the group with higher GDP per capita. Furthermore, the results show that governance quality is an important driver of energy efficiency and, hence, of environmental policies.University of Granad

Enhancement of ferro-para transition in ethanol doped ferroelectric liquid crystals

The influence of ethanol (C2H5OH) doping in the electroclinic liquid crystal has been investigated using dielectric spectroscopy. A giant shift in ferroelectric (SmC∗) to paraelectric (SmA) phase transition has been observed. After analyzing collective relaxation processes, it is confirmed that Curie–Weiss law is obeyed in the vicinity of SmC∗ to SmA phase transition after doping with ethanol. It has been predicted that the dipole-dipole interaction due to ethanol molecules creates the uniformity in the randomized liquid crystal molecules in paraelectric phase, resulting in the increase in the ferroelectric phase in de Vries electroclinic liquid crystal materials

Electrically tunable spatially variable switching in ferroelectric liquid crystal/water system

An unusual switching phenomenon in the region outside conducting patterned area in ferroelectric liquid crystal (FLC) containing about 1–2 wt % of water has been observed. The presence of water in the studied heterogeneous system was confirmed by Fourier transform infrared spectroscopy. The observed optical studies have been emphasized on the “spatially variable switching” phenomenon of the molecules in the nonconducting region of the cell. The observed phenomenon is due to diffusion of water between the smectic layers of the FLC and the interaction of the curved electric field lines with the FLC molecules in the nonconducting region

Study of strontium doping on the structural and magnetic properties of YMnO3ceramics

Structural and Magnetic properties are investigated for the Sr doped YMnO3samples with different composition synthesized by a solid state reaction method. Sr doped YMnO3is the most distorted perovskite of the RMnO3 series (R=rare earths); the observed sinusoidal magnetic structure is in contrast with those exhibited by the less-distorted members, which are commensurate-type antiferromagnetic structures. A typical anti ferromagnetic (AFM) to paramagnetic (PM) phase transition is observed for the sample with concentration x = 0.12 and the Néel temperature (TN) is about 160 K. With decreasing temperature, the sample with x = 0.12 exhibit a magnetic transition from a paramagnetic (PM) to a ferromagnetic (FM) state. © 2013 VBRI press

Synthesis and characterisation of lead free BaFe12O19 –(K0.5Na0.5)NbO3 magnetoelectric composites, and the comparison of various synthetic routes

Polycrystalline lead-free (1-x)BaFe12O19–x(K0.5Na0.5)NbO3 magnetoelectric ceramic composites (x = 10, 20 and 30 wt%) were fabricated for the first time, comparing various synthesis techniques, namely solid state reaction, sol-gel, co-precipitation and citrate combustion methods for the synthesis of the ferrite phase. As well as the four synthesis routes, comparisons were made between uniaxial pressing and cold isostatic pressing of the samples prior to sintering at 1200 °C/2 h. Formation of separate magnetic hexaferrite BaFe12O19 (BaM) and ferroelectric (K0.5Na0.5)NbO3 (KNN) phases in the composites was confirmed using x-ray diffraction. The microstructural features revealed distribution of BaM and KNN grains in all the composite systems. Piezoresponse (PFM) and magnetic force (MFM) modes of scanning probe microscopy (SPM) were utilised to assess responses from piezoelectric and magnetic grains. Localised piezoelectric hysteresis loops were measured on KNN grains in composites made by all four methods. Typical hard magnetic hysteresis loops for BaM were observed exhibiting high coercivity values (up to 281 kA m−1 or 3530 Oe), and those composites made using solid state reaction and citrate combustion methods, which contained no impurity phases, had close to maximum magnetisation values (equivalent to ~70 A m2 kg−1 for the BaM phase). SEM, MFM and magnetisation measurements all suggested that the grain size of the BaM in the composites made using solid state reaction, co-precipitation and citrate combustion methods was around 1 µm, and consisting of single magnetic domains. As a result, it is likely that these samples will exhibit a high degree of magnetoelectric coupling