Charge-balanced codoping enables exceeding doping limit and ultralow thermal conductivity

电荷平衡共掺杂实现超掺杂极限和超低热导率

Materials with low thermal conductivity are applied extensively in energy management,and breaking the amorphous limits of thermal conductivity to solids has attracted widespread attention from scientists.Doping is a common strategy for achieving low thermal conductivity that can offer abundant scattering centers in which heavier dopants always result in lower phonon group velocities and lower thermal conductivities.However,the amount of equivalent heavyatom single dopant available is limited.Unfortunately,nonequivalent heavy dopants have finite solubility because of charge imbalance.Here,we propose a charge balance strategy for SnS by substituting Sn2+with Ag^(+)and heavy Bi^(3+),improving the doping limit of Ag from 2%to 3%.Ag and Bi codoping increases the point defect concentration and introduces abundant boundaries simultaneously,scattering the phonons at both the atomic scale and nanoscale.The thermal conductivity of Ag0.03Bi0.03Sn0.94S decreased to 0.535 W·m^(−1)·K^(−1)at room temperature and 0.388 W·m^(−1)·K^(−1)at 275°C,which is below the amorphous limit of 0.450 W·m^(−1)·K^(−1)for SnS.This strategy offers a simple way to enhance the doping limit and achieve ultralow thermal conductivity in solids below the amorphous limit without precise structural modification.

低导热系数的材料在能源管理中得到了广泛应用,同时突破固体热导率的非晶极限引起了科学家的广泛关注。掺杂是实现低热导率的一种常见策略,它可以提供丰富的散射中心。其中,较重的掺杂剂总是带来较低的声子群速度和较低的热导率。然而,等价的重原子单掺杂的可用元素是有限的。同时,由于电荷不平衡,非等价重掺杂剂的溶解度有限,这限制了其在调控热导率方面的应用。本文在SnS中提出了一种电荷平衡策略,即用Ag^(+)和重Bi^(3+)代替Sn^(2+),将Ag的掺杂限值从2%提高到3%。Ag和Bi共掺杂增加了点缺陷浓度,同时引入了丰富的边界,在原子尺度和纳米尺度上散射了声子。Ag_(0.03)Bi_(0.03)Sn_(0.94)S的热导率在室温下降低至0.535 W·m^(−1)·K^(−1),低于SnS的非晶极限0.450 W·m^(−1)·K^(−1)。该策略提供了一种简单的路径,可以在不进行精确结构修改的情况下,提高掺杂极限并在固体中实现低于非晶极限的超低热导率。