HIGH THERMAL STABILITY OF MICROWAVE DIELECTRIC PROPERTIES OF CaTi_(1-x)(Nb_(1/2)Fe_(1/2))_(x)O_(3)CERAMICS

摘要

This paper presents a study of the structure and microwave properties of Nb_(1/2)^(5+)Fe_(1/2)^(3+) substituted into the Ti4t site of calcium titanate ceramics.The structural and dielectric properties of solid solutions in CaTi_(1-x)(Nb_(1/2)Fe_(1/2))_(x)O_(3),was done.The microwave dielectric properties of solid solutions in CaTi_(1-x)(Nb_(1/2)Fe_(1/2))_(x)O_(3),(CNFTOX with x=0.1 to x=1)is discussed.The modi¯ed CaTiO_(3)(CTO)ceramics were prepared by a new procedure in the solid-state method.A study of the variations of the ball-milling process was done.The calcinations were done at 900C for 3 and 5 h respectively,and the sintering at 1100℃,for 3 h.The structural property studies of the ceramics were investigated by X-ray di®raction(XRD)and Raman spectroscopy.The X-ray analysis showed that all samples have an orthorhombic structure.The renement analysis of all samples were also duly performed and discussed.The nine scattering bands centered at 183,227,247,288,338,470,490 and 805 cm^(-1) were observed.Several peaks presented a small shift as a function of the x value.All Raman spectra in the studied samples showed a small band at 805 cm^(-1),which is a function of the x value.The dielectric permittivity and loss at microwave frequencies(MW)were investigated.For both calcination treatments(900℃for 3 and 5 h),the dielectric permittivity decreased with a decrease of the titanium content.Dielectric permittivity values in the range of 20 to 80 were obtained.It was also observed that a higher number of balls in the milling process contribute to the increase of theεr values.The CNFTO has an excellent microwave property at x=0.6,with a temperature coe±cient of resonant frequency(Tf)near zero(Tf=2.8ppm/℃).