Calcium sulfate and calcium vanadate nanostructures have been synthesized by a hydrothermal route using calcium sulfate and sodium vanadate as the raw materials. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and photoluminescence (PL) spectrum. XRD and SEM observation show that the products are composed of calcium sulfate nanosheets with orhorhombic CaSO4 phase and calcium vanadate nanorods with tetragonal CaV4O9 phase. The size and morphology of the products can be adjusted by controlling the hydrothermal conditions and raw materials. The size of calcium sulfate nanosheets and calcium vanadate nanorods increases obviously with increasing the hydrothermal temperature and reaction time. The formation process of the calcium sulfate and calcium vanadate nanostructures is also discussed. [DOI: 10.1380/ejssnt.2012.585]
Binfeng Zhao,Hongye Wang,Xinwei Xu,Naichao Chen,Jin Cheng,Xiaoyu Li,Hong Wang
The development of fifth-generation (5G)/sixth-generation (6G) mobile system highlights the importance of low-temperature co-fired ceramic (LTCC) technology. However, most medium- ε r ceramics with high quality factors are unsuitable for LTCC technology due to high sintering temperatures. Herein, a series of low-temperature-sintered ZnNb 2 O 6 - x wt.%CaV 2 O 6 ceramics, denoted as ZNO- x wt.%CVO( x =5,7,9,11), characterized by medium permittivity and high quality factors, were prepared by the solid-state reaction method. CaV 2 O 6 exists as a liquid phase during the sintering process. Moreover, liquid-phase sintering is confirmed to be the predominant mechanism for low-temperature densification of ceramics, with evidence from microstructure and activation energy. Ion substitution in the main crystalline phases, induced by ZnNb 2 O 6 –CaV 2 O 6 reaction during the sintering process, causes intrinsic impacts on microwave dielectric properties. Detailed structural analysis allows a comprehensive investigation into the extrinsic and intrinsic effects of CaV 2 O 6 on microwave dielectric properties, including quality factor Q × f , dielectric constant ε r , and temperature coefficient of resonant frequency τ f . Among all compositions, the ZNO-7 wt.% CVO ceramic sintered at 870°C exhibits great properties of Q × f = 57349 GHz, ε r = 21.63, τ f = −70.39 ppm/°C, as well as good chemical compatibility with silver (Ag). Given these advantages, the ZNO-7 wt.%CVO ceramic is a highly promising candidate for medium- ε r LTCC materials in 5G/6G applications.
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