Nanoscale Transition Metal Pnictides: Materials by Design

非技术总结在国家科学基金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，空调消耗了5%的能量，商业制冷高达20%的能量输出。传统的制冷过程(气体压缩和膨胀)效率有限，而且制冷剂往往是消耗臭氧和/或温室气体，一旦出现不可避免的泄漏，就会引起人们的关注。一种更节能(高达50%)且环境友好的工艺是磁制冷，在磁热(MC)材料上施加磁场会导致热释放，而去除磁场会导致热吸收，从而有效地充当热泵。传统的MC材料是以稀土金属Gd为基础的，这种材料在室温下效率较低，而且价格昂贵。在这个由NSF-DMR支持的项目中，将采用一种合理的方法来开发基于纳米颗粒的MC材料，该纳米颗粒包含丰富的地球元素。在开发廉价而高效的磁制冷设备的过程中，将研究纳米颗粒的组成和大小以及颗粒之间的相互作用对磁性的影响。在项目过程中，研究生和本科生将培养批判性思维和技术技能，以及开发下一代先进技术的实践经验。该项目还将通过Go-Girl(获得选择-女孩调查现实生活)材料女孩外联项目向底特律地区的初中和高中女孩介绍材料科学，其中许多女孩是未被充分代表的少数民族。技术总结在国家科学基金会材料研究部的支持下，首席研究人员将生产功能性过渡金属pNictide(pNicogen=第15族元素)纳米粒子和组件，重点关注磁制冷(MR)材料。过渡金属陨石包括一大类但相对未被开发的材料，尽管它们具有跨越能源版图的特性。这些材料正在热电设备(废热转换)、电池(储能)、催化(燃料处理)和磁制冷(气候控制)方面进行研究。这些技术中的许多设想的进步都假定有能力在纳米尺度上控制材料的物理尺寸，这是一个巨大的挑战。此外，对纳米尺度的限制有时会以意想不到的方式影响特性(颗粒内效应)，就像集成/组装(颗粒间效应)一样。这些问题阻碍了过渡金属肽纳米粒子的发展，以解决关键的技术问题。磁流变液是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%，而且更环保，因为它不利用臭氧消耗或温室气体。到目前为止，通过离子交换路线和直接合成，针对铁掺杂的锰多肽，将产生难以获得但很有希望的纳米级MR相(目标1)。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)。这些信息将被用来缩小目标1中生产新材料的参数空间，以便针对最有希望的阶段和尺寸。最后的平行调查(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的材料可用而转移到新阶段。

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.