Ferroelectric materials with high dielectric constant produce high electron emission and the life span of ferroelectric cathodes might be potentially increased if their piezoelectric charge coefficient can be made negligible. For achieving these properties, two different methods were employed to synthesize (Pb0.88La0.12)(Zr0.65Ti0.35)O3 (PLZT12/65/35) ceramics viz., the conventional method (mortar and pestle) followed by uniaxial pressing and the high energy, mechanical activation method (abbreviated to MA, hereinafter). This was done using a high-energy ball mill to reduce particle size drastically. Cold isostatic pressing was used to compact the milled powder which resulted in a significant increase in the density. X-ray diffraction confirmed single phase with cubic perovskite structure. Particle size was measured from TEM images. Morphological studies were carried out by SEM analyses to observe the grain structure. Of these two syntheses methods, PLZT 12/65/35 ceramics prepared via high energy ball milling exhibited significantly higher dielectric constant, surpassing the previously reported values and also exhibited low remnant polarization value, negligible piezoelectric charge coefficient at room temperature. High temperature dielectric measurements at various frequencies confirm the relaxor behavior of PLZT 12/65/35 ceramics. Ferroelectric cathode configuration based on PLZT 12/65/35 ceramics with high relative permittivity allowed us to achieve exceptionally high current density and power obtained in Radio frequency range.