Structural, optical and giant dielectric constant properties of pure ktenasite and schulenbergite/CuO minerals

Abstract

In this study, schulenbergite [(Cu,Zn)7(SO4)2(OH)10·3H2O)]/CuO and pure ktenasite [(Cu,Zn)5(SO4)2(OH)6·6H2O)] minerals were simply synthesized via addition of sodium sulfide (Na2S) to a mixture of nanosized CuO powder dispersed into Zn(NO3)2·6H2O solution. The X-ray diffraction patterns illustrate the formation of schulenbergite/CuO mineral with ratio of 69:31% and 87/13% owing to additions of 0.1 and 0.2 mol L−1 Na2S, respectively. The addition of 0.4 mol L−1 Na2S substance lead to formation of pure ktenasite [(Cu,Zn)5(SO4)2(OH)6·6H2O)] mineral. The absorption vibration modes based on Fourier-transform infrared (FTIR) analysis verified the formation of schulenbergite/CuO and pure ktenasite compositions. The scanning electron microscope micrographs of schulenbergite/CuO and pure ktenasite samples reveal the formation of mixed grains with needle, sheets, cotton and wool shapes. The selected area electron diffraction images of the synthesized powders show strong dot-rings, indicating polycrystalline nature. Optically, all samples possess a high absorption ability for infrared-visible light wavelengths. At lower frequencies, the pellet of pure ktenasite sample exhibits giant dielectric constant characteristics. Exactly, pure ktenasite sample reveals a dielectric constant value of ~ 1.3 × 106 at frequency of 42 Hz. For schulenbergite/CuO (87/13%) sample, a large dielectric constant value of ~ 5311 was measured at frequency of 42 Hz. The colossal and variable relative permittivity values make the pure ktenasite [(Cu,Zn)5(SO4)2(OH)6·6H2O)] mineral is a suggested material for energy storage applications.