A Combination of Calcination and the Spark Plasma Sintering Method in Multiferroic Ceramic Composite Technology: Effects of Process Temperature and Dwell Time

Abstract

This study reports a combined technological process that includes synthesis by the calcination powder route and sintering by the Spark Plasma Sintering (SPS) method for multiferroic ceramic composites in order to find the optimal sintering conditions. The effects of temperature on the SPS process and dwell time on the microstructure and dielectric properties of the PF composites were discussed. Research has shown that using the SPS method in the technological process of the multiferroic composites favors the correct densification of powders and allows for obtaining a fine-grained microstructure with good properties and electrophysical parameters in the composite material. The optimal set of parameters and properties is demonstrated by the sample obtained at the temperature of 900 °C for 3 min, i.e., resistivity (6.4 × 108 Ωm), values of the dielectric loss factor (0.016), permittivity at room temperature (753) and permittivity at the phase transition temperature (3290). Moreover, due to the high homogeneity of the microstructure, the strength of the material against electric breakdown increases (when examining the ferroelectric hysteresis loop, the application of a high electric field (3—3.5 kV/mm) is also possible at higher temperatures). In the case of the composite material tested, both the lower and higher temperatures as well as the shorter and longer dwell times (compared to the optimal SPS process conditions) did not contribute to the improvement of the microstructure or the set of usable parameters of the composite materials. The strength of the ceramic samples against electric breakdown has also diminished, while the phenomenon of leakage current increased.

Influence of the Sintering Method on the Properties of a Multiferroic Ceramic Composite Based on PZT-Type Ferroelectric Material and Ni-Zn Ferrite

“…Fine grains predominate; however, there are also much larger grains, which makes the microstructure heterogeneous in terms of grain size. The sintering conditions used in the SPS method (suitable for other multiferroic composite materials of this type, e.g., [ 32 , 69 ]) do not effectively affect the uniform grain growth for use in the present ferroelectric P component, which results in the formation of internal pores in the sample volume. It decreases the composite sample density.…”

“…The SPS process conditions were as follows: temperature 900 °C, dwell time 3 min, pressure 50 MPa, atmosphere argon gas, heating rate 50 °C/min, and pressing force 4 kN applied uniformly to the die punch during the SPS process. During the SPS process, a number of its technological parameters were recorded, i.e., temperature, time, heating and cooling rates, pressure force, etc., and the changes in the resistance of the sintered material were visualized [ 32 ]. These parameters allowed for selecting optimal parameters for a specific material.…”

“…These parameters allowed for selecting optimal parameters for a specific material. The selection of technological conditions for the SPS process was made based on experimental research presented in previous studies [ 32 , 69 ]. A more detailed description of the SPS method is presented in [ 68 ].…”

“…In addition to searching for new types of multiferroic materials, an intensive search for effective technological methods for their production (synthesis and sintering) to meet these unique requirements has been underway [ 1 , 4 ]. Numerous synthesis methods of ceramic materials are known, e.g., solid-state reaction technique [ 5 , 6 , 7 , 8 ], calcination [ 9 , 10 , 11 , 12 , 13 ], sol-gel [ 14 , 15 ], gel-combustion [ 16 ], mechanochemical activation [ 17 , 18 , 19 , 20 ], and the self-developing synthesis of SHS [ 21 , 22 ], as well as sintering methods, e.g., free sintering (pressureless sintering) [ 23 ], hot pressing [ 24 , 25 , 26 ], microwave sintering [ 23 , 27 , 28 ], spark plasma sintering SPS [ 29 , 30 , 31 , 32 ], and cold-sintering-assisted sintering CSS [ 33 , 34 ]. Well-known methods of synthesis and sintering are used to improve the functional properties of multiferroic materials, which are appropriately modified and combined in the technological process.…”

“…[ 67 ]. In the technological process, several sintering methods are used to obtain multiferroic composite materials, including free sintering (pressureless sintering), hot pressing, and spark plasma sintering [ 32 , 35 , 39 , 40 , 68 , 69 ]. Each of these sintering methods has both numerous advantages as well as disadvantages, whereas not all types of materials subjected to sintering can achieve the desired effect and optimal final properties.…”