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  • 1
    Publication Date: 2018-02-03
    Description: Crystal defects of two synthesized diamonds doped with boron and phosphorus are compared by synchrotron radiation topography (SRT). The crystal defects in the specimen are mainly dislocations. The dislocations are assembled in bundles in the cone-shape and distributed in the directions approximately towards to and . The Burgers vectors of most of the dislocations are parallel to [202] and oblique to the dislocations, showing that the dislocations are of mixed type. The features of the crystal defects are quite different in several aspects compared with the diamonds without phosphorous doping. The ionic radius of phosphorous is 118.75 percent larger than that of carbon and intensive distortion may occur near the phosphorous ions. The dislocations thus originated in bundles to release the stress caused by the phosphorous doping.
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 2
    Publication Date: 2019
    Description: 〈p〉Designing topological and geometrical structures with extended unnatural parameters (negative, near-zero, ultrahigh, or tunable) and counterintuitive properties is a big challenge in the field of metamaterials, especially for relatively unexplored materials with multiphysics coupling effects. For natural piezoelectric ceramics, only five nonzero elements in the piezoelectric matrix exist, which has impeded the design and application of piezoelectric devices for decades. Here, we introduce a methodology, inspired by quasi-symmetry breaking, realizing artificial anisotropy by metamaterial design to excite all the nonzero elements in contrast to zero values in natural materials. By elaborately programming topological structures and geometrical dimensions of the unit elements, we demonstrate, theoretically and experimentally, that tunable nonzero or ultrahigh values of overall effective piezoelectric coefficients can be obtained. While this work focuses on generating piezoelectric parameters of ceramics, the design principle should be inspirational to create unnatural apparent properties of other multiphysics coupling metamaterials.〈/p〉
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
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