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Influence of A-site cation disorder on structural and magnetocaloric properties of Nd_(0.7–x)La_xSr_(0.3)MnO_3(x=0.0, 0.1, 0.2 & 0.3)

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Journal of Rare Earths 2015年第10期33卷 1072-1080页

作者： Sudharshan Vadnala prem pal Saket Asthana Department of Physics Indian Institute of Technology Hyderabad

In the present research, the influence of A-site ionic size disorder on structural, magnetic and magnetocaloric properties of Ndo.7_xtaxSr0.3MnO3 （for x=0.0, 0.1, 0.2 ＆ 0.3） compounds were investigated. These compounds were synthesized by solid state reaction route and crystallized in orthorhombic structure with Pnma space group. An average ionic radius 〈rA〉 increased with La-substitution which influenced the physical properties such as the magnetic entropy varying from 4.78 J/kg.K （for x-=0.0） to 3.55 J/kg.K （for x=0.3） and the maximum magnetization at 5 K changing from 3.92 μB （for x=0.0） to 3.59 μB （for x=0.3）. The change in maximum magnetic entropy decreased with increase of A-site average ionic radius. The decrease in magnetic entropy indicated the suppression of lattice disorder that influenced the spin-lattice coupling. The ferromagnetic transition temperature shifted toward room temperature with La substitution. As 〈rA〉 increased, the phase transition changed from first order （for x-=0.0） to second order （for x≥ 0.1） and the refrigeration capacity increased to a significant level. The modest change in magnetic entropy over a wide range of transition temperature might be useful for future active magnetic refrigeration technology.

关键词： manganites magnetocaloric effect relative cooling Curie temperature rare earths

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A New Model for the Etching Characteristics of Corners Formed by Si<sub>{111}</sub>Planes on Si<sub>{110}</sub>Wafer Surface

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Engineering（科研） 2013年第11期5卷 1-8页

作者： prem pal Sajal Sagar Singh MEMS and Micro/Nano Systems Laboratory Department of Physics Indian Institute of Technology Hyderabad India

The etching characteristics of concave and convex corners formed in a microstructure by the intersection of {111} planes in wet anisotropic etchant are exactly opposite to each other. The convex corners are severely attacked by anisotropic Fetchant, while the concave corners remain unaffected. In this paper, we present a new model which explains the root cause of the initiation and advancement of undercutting phenomenon at convex corners and its absence at concave corners on {110} silicon wafers. This contrary etching characteristics of convex and concave corners is explained by utilizing the role of dangling bond in etching process and the etching behavior of the tangent plane at the convex corner. The silicon atoms at the convex edge/ridge belong to a high etch rate tangent plane as compared to {111} sidewalls, which leads to the initiation of undercutting at the convex corner. On the other hand, all the bonds of silicon atoms pertaining to concave edges/ridge are engaged with neighboring atoms and consequently contain no dangling bond, thus resulting in no-undercutting at concave edges/corners.

关键词： MEMS Silicon Anisotropic Etching Micromachining KOH TMAH Convex Corner Concave Corner

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