Structure and microwave dielectric properties of Sm(2−x)/3Li x TiO3

Abstract

The structural evolution, and microwave dielectric properties of Sm 2Àx ð Þ=3 Li x TiO 3 ceramics (x=0.0≤x≤ 0.5) were investigated in this work. X-ray diffraction (XRD) results show that samples with x>0.3 exhibit a single perovskite phase. Impurity phases of Sm 2 Ti 2 O 7 and TiO 2 appear and their amount increases with the decrease of x when x≤0.3. TEM observation indicates that the A-site is ordered in x=0.5, but not in x=0.3). The dielectric constant decreases with the increase of x for 0.1≤x≤0.4 and then increases with further increase in x up to x=0.5. The Q×f value decreases with the decrease of x due to the increased occurrence of Sm 2 T 2 O 7 secondary phase, defects and twinning boundaries. The temperature coefficient of resonant frequency is negative and its absolute value decreases greatly with the decrease of x value.

Microwave Dielectric Properties of Ca0.8Sr0.2TiO3–Li0.5Sm0.5TiO3 Ceramics with Near-Zero Temperature Coefficient of Resonant Frequency

“…This variation was also observed in CSLNT 11) and many other perovskite seres. 1,6,7) In addition, in our studies, the dielectric constant of CSLST is lower than that of CSLNT with the same proportionate composition because the polarizability decreases from Nd to Sm.…”

“…0:80 exhibited similar crystal structures to the other end member LST, which belong to orthorhombic crystal structural symmetry Pnma (No. 62), 7) whose tilt system was described as a b þ c À in Glazer's notation. 15) The compositional evolution of fundamental perovskite reflections ( ) and the superstructure reflections, indicating A-site cation ordering ( ), antiparallel A-site cation displacement (Ã), in-phase octahedral tilting ( ), and antiphase octahedral tilting ( ), is presented in Fig.…”

“…Dielectric ceramics appropriate for microwave applications as resonators and filters must have a high relative permittivity (" r ) and a high quality factor (Q) at resonant frequencies ( f ) in the gigahertz range as well as a near-zero temperature coefficient of resonant frequency ( f ). 1,2) The composition Ca 0:8 Sr 0:2 TiO 3 (CST) was reported as a promising high dielectric constant and low loss microwave dielectric material with " r ¼ 181 and Q Â f ¼ 6100 GHz, but it has a high positive temperature coefficient of resonant frequency, f ¼ 991 ppm/ C. 3) Compositions in the Li 0:5 Ln 0:5 TiO 3 (Ln: lanthanide; Nd, Sm) (LLT) [4][5][6][7] series were also reported to have high dielectric constants and quality factors with high negative f values such as " r ¼ 80, Q Â f ¼ 2100 GHz, and f ¼ À310 ppm/ C for Li 0:5 Nd 0:5 TiO 3 (LNT) and " r ¼ 52:6, Q Â f ¼ 2650 GHz, and f ¼ À260 ppm/ C for Li 0:5 Sm 0:5 TiO 3 (LST). Mixing positive and negative f materials is the accepted engineering practice for tuning f of a given compound to prepare temperature-stable dielectrics.…”

“…[8][9][10] Both CST and LLT have orthorhombic structures. [3][4][5][6][7] Therefore, LLTs are ideal negative f compounds to mix with CST to create a temperature-stable dielectric.…”

“…Meanwhile, LST also had high microwave dielectric properties with high negative f . 7) Therefore, in this work, LST was used as a negative f compound for mixing with CST to prepare temperature-stable solid solutions. The introduction of LST could induce a change in the tolerance factor (t) of samples because of the decrease in the ionic radius in the A-site.…”