## 1 Introduction  
Multilayer ceramic capacitors (MLCCs) are crucial electronic components used in virtually every area of electronics, and the number and variety of their applications have steadily grown. During the past decade, MLCC manufacturers have been driven to accelerate progress in miniaturization, enhancement of volumetric efficiency, reinforcement of stability and reliability against environment, and cost reduction, none of which can be achieved without an improvement in materials formulation and processing technology. The compositions of most ceramic capacitors are based on ferroelectric barium titanate (BaTiO\({}_{3}\)) materials. BaTiO\({}_{3}\) can be either chemically or physically modified to exhibit the required temperature-stable dielectric behavior [1]. MLCCs used in automobile electronic parts, such as anti-lock brake systems, engine electronic control units, crank angle sensors, and programmed fuel injections, are exposed to high-temperature working conditions of greater than approximately 130 \({}^{\circ}\)C in the engine room of an automobile. MLCCs with X8R specifications (X8R: \(-\)55 \({}^{\circ}\)C to 150 \({}^{\circ}\)C, \(\Delta\)C/C\({}_{25}\)\(\cdot\)c \(\leq\)\(\pm\)15%) were developed to satisfy this requirement. Because of the dramatic variation in permittivity of BaTiO\({}_{3}\) ceramics above the Curie temperature (\(T_{\rm c}\)\(\approx\) 125 \({}^{\circ}\)C), the X8R formulation makes use of the core-shell structure to retain the temperature-stable characteristic by adding rare earth elements with a smaller ionic radius, such as Tm, Yb, Lu, Sc, Er, and Y, to shift the \(T_{\rm c}\) to higher temperatures [2; 3; 4]. Nevertheless, for aerospace, oil drilling, and various other applications, MLCCs in electronic devices must withstand even harsher working environments, typified by temperatures higher than 150 \({}^{\circ}\)C. Accordingly, [PERSON] _et al._ and a few other researchers have recently started to work on the development of dielectric formulations capable of satisfying X9R specifications (\(-\)55 \({}^{\circ}\)C to 200 \({}^{\circ}\)C, \(\Delta\)C/C\({}_{25}\)\(\cdot\)c \(\leq\)\(\pm\)15%) [5; 6; 7; 8; 9; 10; 11]. The utilization of an effective Curie-point shifter, such as (Bi\({}_{0.5}\)Na\({}_{0.5}\))TiO\({}_{3}\) or PbTiO\({}_{3}\), to increase the \(T_{\rm c}\) point along with the formation of the core-shell structure was found to be an effective method for obtaining high-temperature stability [12; 13; 14; 15; 16]. Dielectric formulations, including BaTiO\({}_{3}\)-based compositions, such as BaTiO\({}_{3}\)-(Bi\({}_{0.5}\)Na\({}_{0.5}\))TiO\({}_{3}\)[5; 7; 8; 14; 17; 18; 19], BaTiO\({}_{3}\)-Bi(Zn\({}_{0.5}\)Ti\({}_{0.5}\))O\({}_{3}\)[16; 20], and BaTiO\({}_{3}\)-Pb(Ti\({}_{0.55}\)Sn\({}_{0.45}\))O\({}_{3}\)[10] systems, and (Bi\({}_{0.5}\)Na\({}_{0.5}\))TiO\({}_{3}\)-based compositions, such as (Bi\({}_{0.5}\)Na\({}_{0.5}\))TiO\({}_{3}\)-BaTiO\({}_{3}\)-CaTiO\({}_{3}\)[6; 9; 21] systems, have been developed recently to meet the temperature coefficient of capacitance (TCC) requirements of the X9R specifications. Another approach was a multi-phase composite consisting of a high-\(T_{\rm c}\) material and a low-\(T_{\rm c}\) material. For instance, new X9R dielectrics based on the BaTiO\({}_{3}\)-LiTaO\({}_{3}\) compositions reported by [PERSON] _et al._ can be sintered in a reducing atmosphere and are compatible with the base metal electrode (BME) process [22]. In the BaTiO\({}_{3}\)-(Bi\({}_{0.5}\)Na\({}_{0.5}\))TiO\({}_{3}\) system, (Bi\({}_{0.5}\)Na\({}_{0.5}\))TiO\({}_{3}\) shows strong ferroelectricity at room temperature, undergoes a phase transition with a broad dielectric maximum approximately close to 320 \({}^{\circ}\)C [8], and is considered as an ideal material to shift the Curie temperature of BaTiO\({}_{3}\) above 150 \({}^{\circ}\)C [15].