Nanoscale Transition Metal Pnictides: Materials by Design

非技术总结在国家科学基金会材料研究部的支持下，将实现冷却装置设计的新材料和知识的开发。空调和制冷是日常生活的一部分，空调消耗5%的能源输出，商业制冷高达20%。传统的制冷过程（气体压缩和膨胀）效率有限，制冷剂通常是臭氧消耗和/或温室气体，每当不可避免的泄漏出现时都会引起关注。一个更节能（高达50%）和环境友好的过程是磁制冷，其中将磁场应用于磁热（MC）材料导致热发射，并且去除该场导致热吸收，有效地充当热泵。传统的MC材料是基于稀土金属钆，其在室温附近的效率很差，并且非常昂贵。在这个NSF-DMR支持的项目中，将开发一种合理的方法来开发基于包含地球丰富元素的纳米颗粒的MC材料。 纳米颗粒的组成和大小，以及颗粒之间的相互作用对磁性能的影响将在开发廉价和高效的磁制冷设备的过程中进行研究。 在该项目的过程中，研究生和本科生将培养批判性思维和技术技能，以及尖端技术的实践经验，以开发下一代先进技术。 该项目还将通过GO-GIRL向底特律地区的初中和高中女生介绍材料科学，其中许多女生是代表性不足的少数民族（获得选择-女孩调查真实的生活）物质女孩外展项目。技术总结在国家科学基金会材料研究部的支持下，主要研究者将生产功能性过渡金属磷属元素化物（磷属元素=第15族元素）纳米颗粒和组件，重点是磁制冷（MR）材料。过渡金属磷属元素化物包括大量但相对未被探索的材料类别，尽管具有跨越能量景观的性质。这些材料正在热电装置（废热转换），电池（能量存储），催化（燃料处理）和磁制冷（气候控制）中进行研究。这些技术中的许多设想的进步都假定有能力在纳米级上控制材料的物理尺寸，这是一个重大挑战。此外，限制在纳米尺度上有时会以意想不到的方式影响性能（粒子内效应），整合/组装（粒子间效应）也是如此。这些问题阻碍了过渡金属磷属元素化物纳米颗粒的发展，以解决关键技术问题。 MR基于磁转变过程中能量的吸收和释放（磁热效应），比传统的气体压缩/膨胀系统效率高50%，并且更环保，因为它不使用臭氧消耗或温室气体。因此，将通过利用离子交换路线和直接合成，针对Fe掺杂的Mn pnictides（目标1），产生用于MR的不可接近但有前途的纳米级相。在平行轨道上，将合成阴离子（P，Sb）掺杂的MnAs纳米颗粒，并建立详细的结构-性质-尺寸相关性（目标2）。这些信息将用于缩小Aim 1中新材料生产的参数空间，以瞄准最有前途的相和尺寸。最后的平行研究（目标3）将侧重于整合和评估已知阶段的粒子间相互作用，随后随着目标1和目标2的材料可用而转向新阶段。

NON-TECHNICAL SUMMARYWith support from the National Science Foundation, Division of Materials Research, the development of new materials and knowledge for the design of cooling devices will be achieved. Air conditioning and refrigeration is a part of daily life, with air conditioning consuming 5%, and commercial refrigeration up to 20%, of energy output. The conventional process of refrigeration (gas compression and expansion) has limited efficiency, and the refrigerants are often ozone-depleting and/or Greenhouse gases, raising concerns whenever inevitable leaks arise. A more energy efficient (by up to 50%) and environmentally friendly process is magnetic refrigeration, where application of a magnetic field to a magnetocaloric (MC) material results in heat emission, and removal of that field results in heat absorption, effectively acting as a heat pump. Traditional MC materials are based on the rare-earth metal gadolinium, which suffers from poor efficiency near room temperature and is prohibitively expensive. In this NSF-DMR supported project a rational approach will be exploited for the development of MC materials based on nanoparticles comprising earth-abundant elements. The effect of nanoparticle composition and size, as well as interactions between particles on magnetic properties will studied en route to developing inexpensive and efficient devices for magnetic refrigeration. Over the course of the project, graduate and undergraduate students will develop critical thinking and technical skills, as well as hands-on experience with cutting-edge techniques, for developing the next generation of advanced technologies. The project will also introduce Detroit-area middle and high school girls, many of whom are underrepresented minorities, to materials science through the GO-GIRL (Gaining Options-Girls Investigate Real Life) Material Girls outreach project.TECHNICAL SUMMARYWith support from the National Science Foundation, Division of Materials Research, the principal investigator will produce functional transition metal pnictide (pnicogen = Group 15 element) nanoparticles and assemblies, focusing on materials for magnetic refrigeration (MR). Transition metal pnictides comprise a large but relatively underexplored class of materials, despite having properties that span the energy landscape. These materials are being investigated in thermoelectric devices (waste heat conversion), batteries (energy storage), catalysis (fuel processing), and magnetic refrigeration (climate control). Many of the envisioned advances in these technologies presume the ability to control the physical dimensions of the materials on the nanoscale, a significant challenge. Moreover, confinement to nanoscale dimensions impacts properties in sometimes unexpected ways (intraparticle effects), as does integration/assembly (interparticle effects). These issues have hampered the development of transition metal pnictide nanoparticles to address key technological problems. MR is based on the absorption and release of energy during a magnetic transition (the magnetocaloric effect), and is 50% more efficient than traditional gas compression/expansion systems and more environmentally friendly, as it does not exploit ozone-depleting or greenhouse gases. Heretofore inaccessible but promising nanoscale phases for MR will be produced by exploiting ion-exchange routes and direct syntheses, targeting Fe-doped Mn pnictides (Aim 1). On a parallel track, anion (P, Sb) doped MnAs nanoparticles will be synthesized and detailed structure-property-size correlations established (Aim 2). This information will be used to narrow the parameter space for production of new materials in Aim 1 so as to target the most promising phases and sizes. The final parallel investigation (Aim 3) will focus on integration and assessment of interparticle interactions in known phases, subsequently moving to new phases as materials from Aims 1 and 2 become available.