A new alkali metal–rare earth metal anhydrous sulfate, KTb(SO₄)₂ (KTSO), was synthesized by a hydrothermal method. It crystallized in the non-centrosymmetric (NCS) orthorhombic space group P2₁2₁2₁ with cell parameters a = 5.43950(10), b = 8.8579(3), c = 13.3962(4), Z = 2. Its structure is composed of [KO₁₁], [TbO₈], and [SO₄] groups, which are interconnected to constitute a one-dimensional (1D) chain, and then further linked to construct a three-dimensional (3D) network structure through [SO₄] units. The results of the powder frequency doubling test show that KTb(SO₄)₂ has a phase-matching second-order nonlinear optical effect of 0.3 times that of KH₂PO₄ (KDP). The measured birefringence of the crystal (0.01) agrees well with the calculated value (0.019). Meanwhile, its infrared and ultraviolet spectrum and thermal properties were studied, respectively. Its optical properties and band gap structure are studied by theoretical calculation. This work provides a NCS structure of anhydrous sulfates and offers guidance for further exploration of new anhydrous sulfates.

中文翻译：

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无水硫酸盐 KTb(SO4)2 的合成、晶体结构和非线性光学性质

通过水热法合成了一种新的碱金属-稀土金属无水硫酸盐KTb(SO ₄ ) ₂ (KTSO)。它在非中心对称 (NCS) 正交空间群P 2 ₁ 2 ₁ 2 _{1 中}结晶，晶胞参数a = 5.43950(10), b = 8.8579(3), c = 13.3962(4), Z = 2。其结构由[KO ₁₁ ]、[TbO ₈ ] 和[SO ₄ ] 基团组成，它们相互连接构成一维（1D）链，然后通过进一步链接构建三维（3D）网络结构[所以₄ ] 单位。粉末倍频试验结果表明，KTb(SO ₄ ) ₂具有0.3倍于KH ₂ PO ₄ (KDP)的相位匹配二阶非线性光学效应。晶体的测量双折射 (0.01) 与计算值 (0.019) 非常吻合。同时，分别研究了其红外、紫外光谱和热性能。通过理论计算研究了其光学特性和带隙结构。这项工作提供了无水硫酸盐的 NCS 结构，并为进一步探索新的无水硫酸盐提供了指导。