高硬度硼化钨的结构和异常应力响应

Structure and abnormal stress response of high hardness tungsten borate

自金刚石和立方氮化硼在高温高压下成功实验合成以来,国内外的科学家在寻找新型超硬材料的研究领域展开了大量的探索。由B、C、N和O等轻元素型超硬材料实验合成条件苛刻,而过渡族轻元素型超硬材料的实验和理论探索成为近年来材料、物理和化学等多学科共同关注的热点研究问题。其中,钨硼化合物材料是寻找此类新型超硬材料的重要目标材料之一。与钨原子相比,硼原子的散射截面很小,实验X射线衍射(XRD)图像难以测定钨硼化合物结构和化学组分,这使人们对这些化合物的深入了解受到阻碍,而理论计算研究的方法可以解决这个问题。我们的理论计算研究确定了钨硼体系的热力学稳定结构和大量的亚稳态相,澄清了此前实验合成WxBy结构和组分争议,并预测了一些比之前研究报道更稳定的结构。理想强度计算显示,高硬度硼化钨化合物存在异常应力响应,突破了此前的传统观点,更新了过渡族—轻元素型的高硬度材料的设计理念。

Since first synthesis of diamond and c-BN at high temperature and high pressure,extensive experimental and theoretical efforts have beendevoted to exploring new superhard materialsby the domestic and international scientists.The synthesis of new superhard materials formed by boron(B),carbon(C),nitrogen(N),andoxygen(O)faces littlerate of success,as well as low efficiency,stemming from the fact that these materials canonly be stabilized in a very narrow temperature and pressure regime.Theseshortcomings have prompted anintensive search for alternative materials formed by heavy transition metals and light elements that exhibitexcellent stability and strength but are easier to synthesize.A series ofbinary tungsten borides with relatively easy synthesis conditions are premier prototypes of this new class of superhard compounds.It is difficult to determine the structures of thesecompounds from experimental x-ray diffraction(XRD)data due to the small scattering cross sectionof boron.We explore a wide range of chemical compositions of W-B compounds and establish thermodynamically stable phases,as well as a lot of metastable structures.Our results clarify the previous structural assignments andpredict new structures for possible synthesis.The calculated ideal strength results show that increasing B contentdoes not lead to higher performance on strength and hardness in boron-rich W-B compounds.Our findings challenge the conventionalwisdom and offer key insights into the fundamentalstructural deformation modes and strength for superhard materials.