Gallium nitride (GaN) nanowires and nanotubes possess extraordinary device ability of converting wasted energy into harvestable electricity in terms of their piezoelectricity and pyroelectricity. From the perspective of atomic cohesive energy, we present a model to clarify the physical origin of the size- and shape-dependency of the piezoelectric and pyroelectric properties for intrinsic GaN nanowires and nanotubes. It is shown that both the piezopotential and the pyropotential increase with the inverse of GaN nanocrystal size or with the shape factor. The influence of size and shape becomes more significant for nanotubes with smaller size or wall thick-to-size ratio and may enhance both potentials by up to dozens of times or even more. Such size and shape effects originate from the synergetic effects of nanoscale dielectricity, piezoelectricity and thermoelasticity where the piezoelectricity plays a more important role than the other two factors. Moreover, high piezopotential and pyropotential in GaN nanotubes render them appealing in the design of novel nanogenerators in comparison with the most commonly used nanowires.

氮化镓（GaN）纳米线和纳米管具有非凡的器件能力，就其压电性和热电性而言，它们可以将浪费的能量转化为可收获的电。从原子内聚能的角度出发，我们提出了一个模型来阐明固有GaN纳米线和纳米管的压电和热电特性的尺寸和形状相关性的物理起源。结果表明，压电势和热电势均随GaN纳米晶体尺寸的倒数或形状因子而增加。对于具有较小尺寸或壁厚与尺寸比的纳米管，尺寸和形状的影响变得更加显着，并且可以将两种电势提高多达数十倍甚至更多倍。此类尺寸和形状效应源自纳米级电介质的协同效应，压电性和热弹性，其中压电起着比其他两个因素更重要的作用。此外，与最常用的纳米线相比，GaN纳米管中的高压电势和热电势使其在新型纳米发电机的设计中具有吸引力。