Solid State Chemistry: from Thermoelectric to Nonlinear Optical Materials

热电转换 我的NSERC资助的研究重点是热电转换。随着自然资源的持续减少和人类对电力需求的增加，这种可持续的能源创造方法正变得越来越重要。热电(TE)材料可以通过温度梯度的塞贝克效应产生电能，从而从丰富的余热中产生电能，或者反过来通过帕尔蒂埃效应产生电能的温度梯度。最值得注意的是，自20世纪60年代初以来，这种能源产生方法一直在航天器上使用。自二十多年来，TES一直处于研究的前沿，利用汽车中的余热来减少交流发电机的负荷，从而提高燃料经济性，并在固定应用中利用余热，如光伏和柴火。尽管最近在一些新材料和新策略方面取得了成功，但TE效应的更广泛应用仍然受到相对较低的能量转换效率的阻碍。 材料的TE效率是通过无量纲优值系数ZT来评估的，它取决于塞贝克系数、电导率和热导率(以及温度)。为了获得高效率，材料必须表现出高的塞贝克系数(高的热功率)、高的导电率和低的导热系数。不幸的是，所有这些物理性质都依赖于载流子浓度，因此不能独立优化。我们将专注于四门有前途的材料课程，每一门课程都有不同的挑战需要克服。 非线性光学 第二个新的研究领域是非线性光学(NLO)材料，我们对新的TES的探索导致了潜在的NLO材料的发现。对不同频率的强光的需求超过了市场上现有光源所能提供的。这可以通过使用非线性光学材料来解决，这种材料可以通过上转换或下转换来调制光的频率。一个经典的例子是通过二次谐波产生(SHG)，通过NLO材料实现了从1064 nm到532 nm的倍频(波长减半)。目前，NLO材料正被用于通信系统、遥感、组织成像、环境监测和微创外科手术。红外非线性光学材料的优化是复杂的，因为除了需要较大的二次谐波(SGH)响应外，还需要较高的激光损伤阈值(LDT)、较宽的红外传输范围、较宽的带隙和相位匹配性能。具体地说，带隙越大，LDT越高，但倍频越小。最重要的是，NLO行为存在的一个必要条件是非中心对称空间群。在这里，我们将探索具有良好结构特征的各种主族硫族化合物。

Thermoelectric Energy Conversion My NSERC-funded research is focused on the thermoelectric energy conversion. This sustainable energy creation method is becoming increasingly important, as our natural resources continue to decline and mankind's need for electricity increases. Thermoelectric (TE) materials can create electricity via the Seebeck effect from a temperature gradient, and thus from the abundant waste heat, or in turn create a temperature gradient from electricity via the Peltier effect. Most notably, this method of energy generation has been in continuous use in spacecrafts since the early 1960s. Since the better of two decades, TEs have been at the forefront of research into utilizing the waste heat in automotives to reduce the load on the alternator and thereby enhance fuel economy, and for waste heat utilization in stationary applications such as photovoltaics and wood-stoves as well. More widespread applications of the TE effect are still hindered by the comparatively low energy conversion efficiency despite recent success with a number of new materials and strategies. The TE efficiency of a material is evaluated by the dimensionless figure-of-merit, zT, which depends on the Seebeck coefficient, the electrical conductivity, and the thermal conductivity (as well as the temperature). To obtain high efficiency, the materials must exhibit high Seebeck coefficient (high thermopower), high electrical conductivity but low thermal conductivity. Unfortunately all these physical properties depend on the charge carrier concentration, and can therefore not be independently optimized. We will focus on four promising materials classes, with each having different challenges to overcome. Nonlinear Optics A second, new research area is in nonlinear optical (NLO) materials, after our search for new TEs resulted in discovering potential NLO materials. The demand for intense light at various frequencies exceeds what current light sources on the market can deliver. This may be solved by using NLO materials that can modulate the frequencies of light via up-conversion or down-conversion. A classical example is frequency doubling (halving the wavelength) of a Nd:YAG laser from 1064 nm to 532 nm through an NLO material via the second harmonic generation (SHG). Currently NLO materials are being used in communication systems, remote sensing, tissue imaging, environmental monitoring, and minimally invasive surgeries. The optimization of IR NLO materials is complex, for one needs - in addition to a large second-order harmonic generation (SGH) response - also a high laser damage threshold (LDT), a wide IR transmission range, a wide band gap, and phase matching behavior. Specifically, a larger band gap generally results in a higher LDT but smaller SHG. On top of that, a necessary criterion for the existence of NLO behavior is a noncentrosymmetric space group. Here we will explore various main group chalcogenides with promising structural features.