Relations between the bandgap and structural properties and composition of the M–Si–N nitridosilicates (M = alkali, alkaline earth or rare earth metal) have been obtained, using experimental data collected from literature; and qualitative models are presented to explain the observed trends. Compounds with a higher degree of condensation, i.e. a higher Si/N ratio, generally have longer M–N bonds and shorter Si–N bonds. The observations can be explained based on the effective charge of N, dependent on its coordination with Si (NSi_x). With increasing Si/N ratio the coordination number of N by Si increases, making the effective charge of the nitrogen atom less negative, resulting in a longer and less covalent M–N bond. This also shifts the N 2p levels down in energy, lowering the top of the valence band (mainly composed of N orbitals); while decreasing the Si–N distance shifts the bottom of the conduction band (mainly composed of Si and M orbitals) upward. Some nitridosilicates show deviations to the general trends, such as γ-Si₃N₄ and several Li-containing compounds. These deviations have been discussed and possible explanations have been given based on peculiarities in their structural characteristics.

中文翻译：

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关于N–Si–N（M =碱金属，碱土金属或稀土金属）氮化硅酸盐的能隙，结构和组成之间的关系

利用从文献中收集到的实验数据，获得了M–Si–N氮化硅酸盐（M =碱金属，碱土金属或稀土金属）的能带隙与结构性质和组成之间的关系。并提出了定性模型来解释观察到的趋势。具有较高缩合度（即较高的Si / N比）的化合物通常具有较长的M–N键和较短的Si–N键。可以根据N的有效电荷来解释这些观察结果，这取决于N与Si（NSi _x）。随着Si / N比的增加，Si的N配位数增加，从而使氮原子的有效电荷变少，从而导致更长的共价M-N键越来越少。这也使N 2p能级下降，降低了价带的顶部（主要由N个轨道组成）；同时减小Si–N距离会使导带的底部（主要由Si和M轨道组成）向上移动。一些nitridosilicates显示偏差的一般趋势，如γ-的Si ₃ Ñ ₄和几个含Li的化合物。已经讨论了这些偏差，并根据其结构特征的特殊性给出了可能的解释。