Stuffed Tridymite Structures: Synthesis, Structure, Second Harmonic Generation, Optical, and Multiferroic Properties

Synthesis, Optical, Dielectric, SHG, Magnetic and Visible Light Driven Catalytic Studies on Compounds Belonging to the Swedenborgite Structure

A new compound, InBaZn3 GaO7 , with swedenborgite structure along with transition metal (TM) substituted variants have also been prepared. The structure contains layers of tetrahedral ions (Zn2+ /Ga3+ ) connected by octahedrally coordinated In3+ ion forming the three-dimensional structure with voids where the Ba2+ ions occupy. The TM substituted compounds form with new colors. The origin of the color was understood based on the ligand-field transitions. The near IR reflectivity studies indicate that the Ni - substituted compounds exhibit good near - IR reflectivity behavior, making them possible candidates for 'cool pigments'. The temperature dependent dielectric studies indicate that the InBaZn3 GaO7 compound undergoes a phase transition at ~360 °C. The compounds are active towards second harmonic generation (SHG). Magnetic studies show the compounds, InBaZn2 CoFeO7 and InBaZn2 CuFeO7 to be anti-ferromagnetic in nature. The copper containing compounds were found to be good catalysts, under visible light, for the oxidation of aromatic alkenes. The many properties observed in the swedenborgite structure-based compounds suggests that the mineral structure offers a fertile ground to investigate newer compounds and properties.

Crystal Structure and Ferroelectric Evidence of BaZnSi3 O8 , a Low-Permittivity Microwave Dielectric Ceramic

BaZnSi₃ O₈ ceramic was prepared by the conventional solid-state method and sintered at 1100 °C. XRD and synchrotron Rietveld refinement analyses revealed the BaZnSi₃ O₈ ceramic presented a monoclinic structure with a space group of P2₁ /a (No.14), which is reported for the first time. The BaZnSi₃ O₈ ceramic presented a weak ferroelectricity, which was confirmed by the P-E loop and the 90° nanoscale ferroelectric domain. Although ϵ_r -T displayed two ϵ_r abnormal peaks at 400 °C and 460 °C, the Curie temperature (T_c ) was located at 460 °C according to the dielectric loss and Curie-Weiss law. Moreover, the BaZnSi₃ O₈ ceramic exhibited optimized microwave dielectric properties with ϵ_r =6.55, Q×f=52400 GHz, and τ_f =-24.5 ppm/°C. Hence, the BaZnSi₃ O₈ ceramic in the ternary BaO-ZnO-SiO₂ system possessed both weak ferroelectricity and microwave dielectric properties. These results are expected to break the technical barrier of ferroelectric phase shifter applications in microwave and even millimeter-wave frequency bands.