Cold sintering of calcium titanate-based material

Objectives. The work set out to obtain materials based on calcium titanate via cold sintering process (CSP) using magnesium sulfate hydrate as an activating additive and study the phase composition, microstructure, integral structural characteristics, and dielectric properties of the obtained materials depending on the activating additive fraction and the CSP temperature.

Methods. CaTiO₃-based materials with additions of MgSO₄·6H₂O (5–15 mol %) having an open porosity of at least 10% were obtained via CSP using uniaxial compression at a pressure of 220 MPa, temperatures from 300 to 400°C, and isothermal holding for 1 h.

Results. A formation mechanism of the material under the specified conditions is proposed, including stages involving a predominance of dissolution–precipitation and solid-phase diffusion mechanisms. With the addition of 5–10 mol % of MgSO₄·6H₂O, the dielectric loss tangent tanδ is ~0.01, while the relative permittivity ε_r is 38–52 at frequencies from 500 kHz to 2 MHz. Increasing the CSP time to 2 h at 400°C leads to an increase in ε_r to 50. Subsequent calcination in air at 900°C for 3 h leads to an increase in ε_r to 62 and a decrease in tanδ to 0.004. The decrease in the ε_r value of all the obtained materials as compared to pure CaTiO₃ (ε_r = 150–170) is due to high open porosity values (at least 10%).

Conclusions. A calcium titanate–based material via CSP can be produced using magnesium sulfate hydrate as an activating additive. CSP gives a porous material with high frequency stability, ε_r = 38–62, and tanδ ~ 10⁻² –10⁻³ . Due to their high open porosity, the resulting materials are promising for use as frameworks for composite capacitor materials.

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