Investigation of the Anisotropic Thermal Expansion Mechanism of Ag_xGa_xGe_1–xSe₂ Crystals

Abstract

Quaternary nonlinear optical single crystals Ag x Ga x Ge1–x Se2 (x = 0.250, 0.167) were grown by the Bridgman method in a four-zone furnace. The thermal expansion behavior of Ag x Ga x Ge1–x Se2 (x = 0.25, 0.167) was studied by the method of single-crystal X-ray diffraction from 150 to 295 K and powder X-ray diffraction in the range of 298–773 K. Both results show the crystals have positive linear thermal expansion coefficients in different directions and a positive volume thermal expansion coefficient, and it is observed that they satisfy the relationship of α a > α c > α b and α V ≈ α a + α b + α c for the orthorhombic structure. It is found that the Ag x Ga x Ge1–x Se2 (x = 0.25, 0.167) unit cells varying with temperature were mainly dominated by variations in framework geometry (AgSe4 tetrahedron), and the thermal motion of Ag atoms in the AgSe4 tetrahedron. As it was revealed, according to the powder X-ray diffraction, it is found that the isotropic thermal atomic displacement parameter of the Ag atoms is much larger than those of the Se and Ga­(Ge) atoms in the AgSe4 tetrahedron. Furthermore, anisotropic atomic displacement parameters (ADPs) of Ag atoms are extracted from the single-crystal diffraction; the ADPs along the a axis, b axis, and c axis have a significant difference, which means the thermal vibration of Ag atoms is anisotropic. It is of great significance for improving crystal growth technology and understanding the thermal properties of this kind of crystals.

Meltable Aluminum Molecular Rings with Fluorescence and Nonlinear Optical Properties

“…Their thermal expansion coefficient was between inorganic compounds and some MOFs. [2,[31][32] We collected SCXRD data at 80, 160, and 298 K to discuss the changes in the supramolecular structures when heated and investigate whether this positive thermal expansion affected the interaction force between molecules in the crystal. As shown in Figure 2c, the organic components present in both the rings and free objects underwent a certain degree of thermal vibration, rotation, and deformation.…”

“…This implies that the thermal expansion along the c‐axis was higher than that along the other two axes. Their thermal expansion coefficient was between inorganic compounds and some MOFs [2,31–32] …”

Crystal Growth, Characterization, and Properties of Nonlinear Optical Crystals of LixAg1–xGaSe2 for Mid-Infrared Applications

“…Therefore, they play a pivotal role in various applications, including environmental monitoring, atmospheric transmission, minimally invasive surgery, spectroscopy, and imaging. 2 So far, commercially available mid-IR NLO crystals generally comprise AgGaS 2 , AgGaSe 2 , and ZnGeP 2 , 3−5 which show advantages of large NLO coefficients (13,33, and 75 pm/V 6 ) and wide-infrared transmission range. However, the laser-induced damage threshold (LIDT) of AgGaS 2 and AgGaSe 2 is relatively low, 7 hindering application in highpower laser output.…”

“…Thus, the properties of materials can be adjusted by ion substitution to form a solid solution or compound to achieve such an equilibrium. AgGaGe n S 2( n +1) and AgGaGe n Se 2( n +1) are quaternary solid solution crystals obtained by replacing Ga 3+ with Ge 4+ in AgGaS 2 and AgGaSe 2 crystals, − which increased the LIDT several times while maintaining the large NLO coefficient.…”

Crystal Growth, Characterization, and Thermal Annealing of Nonlinear Optical Crystals AgGaGenSe2(n+1) (n = 1.5, 1.75, 2, 3, 4, 5, and 9) for Mid-infrared Applications

“…In the first publication, seven compounds ( n = 1.5, 1.75, 2, 3, 4, 5, and 9) were characterized, and then the phase diagrams of AgGaSe 2 –GeSe 2 and Ag 2 Se–Ga 2 Se 3 –GeSe 2 system were investigated to reveal the reaction mechanism. , Although the structure and phase diagrams have been almost fully understood, there are still few reports on the growth and application of AgGaGe n Se 2( n +1) . Until now, only a few compounds including AgGaGe 3 Se 8 , AgGaGe 4 Se 10 , and AgGaGe 5 Se 12 − have been studied as NLO crystals.…”