A Study of the Effect of Sintering Conditions of Mg0.95Ni0.05Ti3 on Its Physical and Dielectric Properties

Mg0.95Ni0.05TiO3 ceramics were prepared by traditional solid-state route using sintering temperatures between 1300 and 1425 °C and holding time of 2–8 h. The sintered samples were characterized for their phase composition, micro-crystalline structure, unit–cell constant, and dielectric properties. A two-phase combination region was identified over the entire compositional range. The effect of sintering conditions was analyzed for various properties. Both permittivity (εr) and Q factor (Qf) were sensitive to sintering temperatures and holding times, and the optimum performance was found at 1350 °C withholding time of 4 h. The temperature coefficient of resonant frequency (τf) in a range from −45.2 to −52 (ppm/°C) and unit–cell constant were not sensitive to both the sintering temperature and holding time. An optimized Q factor of 192,000 (GHz) related with a permittivity (εr) of 17.35 and a temperature coefficient (τf) of −47 (ppm/°C) was realized for the specimen sintered at 1350 °C withholding time of 4 h. For applications of 5G communication device (filter, antennas, etc.), Mg0.95Ni0.05TiO3 is considered to be a suitable candidate for substrate materials.

Magnetic ordering in double perovskites with 4d and 5d elements

B-site ordered double perovskites of the type AA′BB′O6 have attracted attention recently due to unusual and unpredictable modes of magnetic order. Of particular interest are materials where AA′ = Ba, Sr or La and B′ = Mo,Ru,Os and Re and B is a diamagnetic ion such as Li+,Na+,Ca2+, Mg2+, Zn2+ or Cd2+.Crystal symmetries encountered are Fm-3m, I4/m and P21/n as a function of the Goldschmidt tolerance factor which in turn impose local symmetries at the magnetic B′ site of m-3m, 4/m and -1, respectively. The magnetic ions have electronic configurations 4d1, 4d3,5d1, 5d2 and 5d3 with nominal spins, S = 1/2,1 and 3/2. Spin orbit coupling is very large, reaching ~ 0.5eV for the 5d ions, and plays a more important role than in the more familiar 3d-based magnetic materials. Geometric frustration, the B′ ion sublattice is f.c.c., based on edge sharing tetrahedra, also is of critical importance. Observed magnetic ground states range from spin glasses (without apparent disorder), collective spin singlets, ferromagnets and antiferromagnets. Often, ordered moments are a small fraction of a Bohr magneton. Systematic behavior is elusive. For example Ba2YReO6 and Ba2CaOsO6 (both Fm-3m) have the same unit cell constant to within .01 % and both are based on 5d2 ions but the former is a highly unconventional spin glass and the latter orders antiferromagnetically below 50K. Recent results on this class of magnetic materials will be described in the context of existing theories.

Effect of Tb3+-Coped Concentration on Properties of Li2SrSiO4:Tb3+ Phosphor

A series of Tb3+-doped Li2SrSiO4phosphors were prepared by high temperature solid state reaction. Effect of Tb3+-coped concentration on luminescence properties of Li2SrSiO4: Tb3+phosphor was investigated by XRD, FTIR, PL and CEI measurements. The results showed that the unit cell constant of Li2SrSiO4:Tb3+was reduced gradually with increasing Tb3+concentration, and then the FTIR absorption intensity assigned to the stretch vibration of [SiO4] and bend vibration of Si-O was decreased. The emission properties of Li2SrSiO4:Tb3+phosphors are strongly dependent on the concentration of Tb3+. The stronger blue and weaker green emission were shown as adding 1% Tb3+amount, while single bright green emission was presented in 20% Tb3+contents. The corresponding CIE was observed from (0.192, 0.315) to (0.246, 0.599). The results showed that the luminescence properties of Li2SrSiO4:Tb3+phosphor could meet various requirements by tuning the Tb3+-doped concentration.

Analysis of Antimony-Tin-Based Skutterudites

Since the proposal of skutterudites as possible Phonon-Glass, Electron-Crystal materials, a lot of work has been done trying to fill the structural voids with foreign “rattling” atoms. In order to keep the electronic count per unit cell constant (and thus, the semiconducting properties of most of the compounds under study) partial replacement of either the cation or the anion in the original formula by an appropriate neighbor in the periodic table is an option. In the case of antimonides, replacing part of the Sb with Ge or Sn in order to compensate the extra charge introduced by void fillers has proved useful for compounds based on rare-earth filled IrSb3. In the case of RhSb3, we found that large quantities of Sn can be incorporated into the skutterudite structure of RhSb3 without either filling the voids or producing charge carriers.We have analyzed the stability of several cross-sections of the Rh-Sb-Sn ternary system and have found a wide range of compositions with the basic skutterudite structure as we vary the Sn content. In all the cases, the tin goes substitutionally into the antimony sites. The voids remain empty. Density measurements suggest the existence of metal vacancies, confirmed by Rietveld refinement of the powder X-ray diffraction patterns. The possibility of Sn-induced mixed-valence of Rh on the anion sites is being investigated.