Crystal-structure refinement of Sr3Ga2Ge4O14

Abstract

The accurate X ray diffraction study of a Sr 3 Ga 2 Ge 4 O 14 crystal was performed based on two X ray diffraction data sets collected on a diffractometer equipped with a CCD area detector (a = 8.2776(2), c = 5.0415(1) Å, sp. gr. P321, Z = 1, R/wR = 0.78/0.69%, 3645 independent reflections). The structure of Sr 3 Ga 2 Ge 4 O 14 is characterized by the presence of two mixed cation sites, which is accompanied by the anhar monic motion not only of cations, but also of two oxygen atoms in general positions. The structures and elec tromechanical characteristics of Sr

Synthesis and Characterization of the New Strontium Borogermanate Sr3–x/2B2–xGe4+xO14 (x = 0.32)

“…The strontium cation in the center of the polyhedron is displaced along the a axis from the short O2–O2 edge shared with the germanium octahedron (position 1 a ) toward the longer O1–O1 edge (Figure b). The observed bond angels and lengths within the structure are in good agreement to those of other borogermanates and the isotypic phase Sr 3 Ga 2 Ge 4 O 14 . ,,,,, …”

“…On the other side, the longest edge within the dodecahedron of Sr 3– x /2 B 2– x Ge 4+ x O 14 ( x = 0.32) is increasing to a value of 463.7(4) pm in comparison with 415.7(2) pm in the dodecahedron of Sr 3 Ga 2 Ge 4 O 14 . These differences in the length can be interpreted as a result of the formal substitution of gallium through boron (boron occupies the Ge site 2d and Ge occupies the original mixed Ga/Ge sites) . As the size of the dodecahedron around the special site 3 e is crucial for the piezoelectric properties, this expansion of the structure of Sr 3– x /2 B 2– x Ge 4+ x O 14 ( x = 0.32) along [100] compared to Sr 3 Ga 2 Ge 4 O 14 could cause better piezoelectric properties. ,, …”

“…This class of compounds is highly interesting concerning their piezoelectric properties because nearly all 140 known members crystallize in the trigonal noncentrosymmetric space group P 321. , As opposed to commonly used piezoelectric materials such as quartz or lithium niobate (LiNbO 3 ), several members of the langasite family do not show any phase transition until their melting point around 1500 °C. This high-temperature stability as well as the good piezoelectric properties led to a high scientific and practical interest in these materials being ideal for high-temperature and high-sensitivity applications such as surface acoustic wave (SAW) or bulk acoustic wave (BAW) sensors. − …”

Growth and X-ray Diffraction Study and Specific Features of Thermal Expansion of Ba3NbFe3Si2O14 Single Crystal from the Langasite Family

“…When refining the standard model of spherical atoms in the harmonic approximation, peaks with amplitudes as large as 1.1 e/Å 3 were found near atoms in the difference electron-density map. To describe this disordering of atomic sites in the BNFS structure, the anharmonic atomic displacement parameters (ADPs) were used. , The optimal anharmonic model was sought by using the “anharmonic displacement expert”, the technique of its application is described in refs and . The atomic displacements in the 3 e , 1 a , 3 f , and also O2­(6 g ) and O3­(6 g ) sites at 293 K were characterized by anharmonic tensors (model 3342234, labeling from).…”

“…18 The anharmonicity of atomic displacements in La 3 Ga 5 SiO 14 as a measure of disordering and a possible precursor of phase transformations was observed for the first time in ref 19. Then, as the accuracy and reliability of results increased, it was found in a number of langasite-family compounds, 20,21 which were investigated using the approach of intermeasurement minimization (i.e., by a comparison of experimental data obtained under different experimental conditions). 22 In several studies, the attempts to use another symmetry group, except P321, were unsuccessful due to objective reasons of the low accuracy of these studies.…”