Preparation And Properties Of CaTiO₃-Li_1/2Nd_1/2TiO₃ Microwave Dielectric Ceramics With High Dielectric Constant

CaTiO₃ ceramics have a high dielectric constant（ε_r=170）and low dielectric loss（Q×f=3600GHz）.However,they also show a large positiveτ_f value of+800ppm/℃.By adding Li_1/2Nd_1/2TiO₃（τ_f=-310ppm/℃）to adjust theτ_f value,the dielectric constant and quality factor of the CT-LNT ceramics always decreased quickly.CT-LNT ceramics were prepared through the conventional solid-state reaction method.Attempts were made to solving these problems,such as A and B-site ion substitution,adding additives.The phase composition,microstructure and microwave dielectric properties of CT-LNT based ceramics have been investigated.The main content is as following:1.（1-x）CaTiO₃-xLi_1/2Nd_1/2TiO₃ ceramics were prepared through the conventional solid-state reaction method.Theτ_f value was tuned to near zero with x increasing,while theε_r and Q×f value decreased.When x=0.8,the（1-x）CaTiO₃-xLi_1/2Nd_1/2TiO₃ceramics sintered at 1275℃ exhibited microwave dielectric properties:ε_r=123.1,Q×f=1680GHz,τ_f=+31.2 ppm/℃.The ceramics with Sr²⁺ion doping resulted in the increase ofε_r value and decrease of dielectric loss.The microwave dielectric properties ofε_r=132.3,Q×f=2310GHz,τ_f=+52.2ppm/℃were obtained for the speicmen 0.2Ca_15/16Sr_1/16TiO₃-0.8Li_1/2Nd_1/2TiO₃ ceramics sintered at 1250℃for 4h.2.Bi₄B₂O₉ was added to adjust theτ_f of 0.2Ca_15/16Sr_1/16TiO₃-0.8Li_1/2Nd_1/2TiO₃ceramics.With the addition of Bi₄B₂O₉,the temperature coefficient of resonant frequency of the ceramics can be effectively adjusted,while the high value ofε_r and Q×f were maintained stably.A near zeroτ_f（τ_f=-7.7ppm/℃）withε_r=128.8,Q×f=2280GHz was obtained for 5wt%Bi₄B₂O₉ doped ceramics sintered at 1250℃,3.The Li_1/2Nd_1/2TiO₃ with negativeτ_f was added as compensators,and（Ca,Ln）TiO₃-Li_1/2Nd_1/2TiO₃ ceramic were investigated using Ln³⁺（Ln:La,Nd,Sm）to substitute A-site ion.Nd³⁺ion substitute can increase the Q×f value and the high value ofε_r was maintained stably.La³⁺ion substitute can increase theε_r value,while the dielectric loss increase as well.Sm³⁺ion substitute can increase the Q×f value and theτ_f value was adjusted to zero,but it had a lowε_r value.A series of microwave dielectric ceramics with a highε_r value（ε_r≥90）and good microwave dieletric properties were obtained.Excellent microwave dielectric properties ofε_r=123.5,Q×f=2610 GHz,τ_f=+23.6 ppm/℃ were obtained for the0.4Ca_0.61Nd_0.26TiO₃-0.6Li_1/2Nd_1/2TiO₃ ceramics sintered at 1250℃ for 4h.Besides,the effect of Sn⁴⁺substitute B-site ion on the microwave dielectric properties of the0.4Ca_0.61Nd_0.26TiO₃-0.6Li_1/2Nd_1/2TiO₃ ceramics was investigated.The dielectric constant decreased and the quality factor increased with SnO₂ adding.When x=0.07,0.4Ca_0.61Nd_0.26Ti_1-xSn_xO₃-0.6Li_1/2Nd_1/2TiO₃ ceramics sintered at 1250℃ for 4h showed dielectric properties ofε_r=119.2,Q×f=2840GHz,τ_f=+36.1ppm/℃。.4.Li¹⁺was easily to be volatilized during high temperatures processing,so excess Li was added through two separate ways to compensate the evaporation of Li.The effect of excess of Li on microwave dielectric properties and microstructure was investigated.The excess Li₂CO₃ was added when synthesised Li_1/2Nd_1/2TiO₃ powders,which can increase the dielectric constant and lower sintering temperature.Nevertheless,the Q×f values decreased.On the other way,the excess Li₂CO₃ was added as an additive.The dielectric constant increases and the high value of Q×f were maintained stably with appropriate Li₂CO₃ added.The microwave dielectric properties ofε_r=128.3,Q×f=2630GHz,τ_f=+39.1ppm/℃were obtained for the0.4Ca_0.61Nd_0.26TiO₃-0.6Li_1/2Nd_1/2TiO₃ ceramics with 3mol%Li₂CO₃ addition sintered at 1250℃ for 4h.