Improvements and Modifications to Room‐Temperature Fabrication Method for Dielectric Li₂MoO₄ Ceramics

Abstract

Dielectric properties of lithium molybdate disks fabricated by moistening water-soluble Li 2 MoO 4 powder, compressing it, and postprocessing the samples at 120°C, were improved by the optimization of powder particle size, sample pressing pressure, and postprocessing time. It appeared that the postprocessing temperature of the Li 2 MoO 4 ceramics could be chosen so as to be applicable to the associated integrated materials as long as the postprocessing time was adequately adjusted to ensure the removal of the residual water. In addition, the dielectric properties of Li 2 MoO 4 ceramic were modified with an inclusion of suitable additives. For example, at 1 GHz the relative permittivity of Li 2 MoO 4 disks fabricated at room temperature and postprocessed at 120°C was increased from 6.4 to 8.8 with an addition of 10 vol% of rutile TiO 2 and to 9.7 with an addition of 10 vol% of BaTiO 3 . At the same time the loss tangent value increased from 0.0006 to 0.0014 and to 0.011, respectively.

3D printed dielectric ceramic without a sintering stage

“…When permittivity values of 5.59 for Li 2 MoO 4 (after porosity correction by equation (2), see Methods) and 1 for air were used, the resulting calculation gave theoretical permittivities of 4.4–4.7 which deviated only slightly from the measured values. The measured dielectric loss values had the same magnitude of (10 −4 ) as those measured for samples manufactured with RTF 22 and sintering 20 . However, the dielectric properties achieved make this fabrication method feasible for high frequency applications, especially if complex shapes are needed.…”

“…However, the dielectric values were reasonable although the densities remained lower compared to those reported earlier for Li 2 MoO 4 parts manufactured by simple pressing and drying (RTF) 22 or pressing and sintering 20 . The theoretical relative permittivity of dielectric media with high porosity can be estimated by the Maxwell-Garnett equation 49 (equation (1), see Methods).…”

“…These factors determine the feasibility of the material in different electrical applications 35,36 . The measured densities and dielectric properties are reported in Table 1 in comparison with those reported for Li 2 MoO 4 parts manufactured with RTF and post-processing at 120 °C 22 , and sintering at 540 °C 20,37 . It should be noted that the dielectric properties were measured from the samples thinned evenly from the bottom and top sides (thickness 0.87–0.94 mm) due to the requirements of the dielectric properties measurement device (see Methods).…”

“…Post-processing at 60 °C and 120 °C, for 24 and 6 h respectively, was employed to speed up the evaporation of the water and to ensure complete drying 22 .…”

“…The dissolved Li 2 MoO 4 recrystallizes during drying due to water evaporation, which can be speeded up by heat treatment at 120 °C 21 . The RTF method has also been applied in the manufacture of Li 2 MoO 4 based composites to tailor the relative permittivity 22,23 and its thermal coefficient 23 , or to introduce magnetic properties 25 . As no sintering is required, the unwanted formation of extra phases or heat expansion mismatch between the materials are not observed.…”