Among the KCoO 2 -type phases, the orthorhombic layered nitride CaTiN 2 is a newly reported high dielectric permittivity material (ε r ∼ 1300−2500 within 10 4 −10 6 Hz from 80 to 450 K) while the tetragonal SrTiN 2 is reported to display an unintentional metallic conduction property. In this work, a Ca 1−x Sr x TiN 2 solid solution was synthesized, in which the insulating SrTiN 2 end member and some Sr-doped CaTiN 2 samples were successfully obtained, and therefore, the dielectric properties of the Ca 1−x Sr x TiN 2 solid solution were investigated. The Sr substitution for Ca drove an orthorhombic-to-tetragonal phase transformation in Ca 1−x Sr x TiN 2 , which reduced the dielectric permittivity significantly. The tetragonal SrTiN 2 displays a much lower dielectric permittivity (ε r ∼ 20−70 in 10 5 −10 6 Hz and 10−300 K) than that of CaTiN 2 . The comparison on the dielectric permittivities and structures of CaTiN 2 and SrTiN 2 indicates that the structural distortion arising from the splitting of N planes between Ti layers within the TiN 2 pyramidal layers could be a plausible structural origin of the high bulk dielectric permittivity of CaTiN 2 .

A facile method to prepare the stable, highly siliceous Ti-UTL zeolite with extra-large pores via hydroxyl free radical (˙OH) assisted isomorphous substitution of Si for Ge under mild conditions.

Phase transition−structure−dielectric properties in microwave band correlations were determined for the (Sm 1−x Ca x ) (Nb 1−x Mo x )O 4 (SNCMo@x) system. X-ray and Raman analyses along with selected-area electron diffraction indicated that SNCMo@x (0.15 ≤ x < 0.375) ceramics crystallize in the I2/a space group (monoclinic fergusonite), whereas the I4 1 /a space group (tetragonal scheelite) best describes SNCMo@x (0.375 ≤ x ≤ 0.7), suggesting that the increased ionic radius of the A-site effectively contributed to the ferroelastic phase transition and ensures the stability of the scheelite phase. The SNCMo@x ceramic materials exhibit composition-dependent permittivity (ε r ) with a distribution between 12.0 and 17.7. The distortion and deformation of the [BO] polyhedra should be responsible for the shift from negative to positive temperature coefficient of resonant frequency (TCF) and the irregular behavior of the quality factor (Q × f). An optimum microwave dielectric performance was achieved for SNCMo@0.18 (ε r ∼ 17.1, Q × f ∼ 52, 800 GHz at ∼8.80 GHz, and TCF ∼ −1.4 ppm/°C). This work demonstrates the important role of simultaneous substitution of A/ B cations on [BO] polyhedral distortion and deformation in RENbO 4 materials and its significant effect on the microwave dielectric properties. Also, the SNCMo@0.18 ceramic has been designed as a cylindrical dielectric resonator antenna with a high simulated radiation efficiency (97.1%) and gain (5.96 dBi) at the center frequency (7.75 GHz), indicating its promising application in X-band satellite communication (7.62−7.89 GHz) because of its adjustable permittivity, low loss, and good temperature stability.

Polycrystalline samples, prepared by a solid-state route, of compositions in the solid solution CeMnCoGeO (x = 0.0, 0.5, 1.0, 1.5, and 2.0) were characterized by X-ray diffraction, neutron diffraction, and magnetometry. They adopt space group P4/nbm with a ≈ 9.78 and c ≈ 4.85 Å and become anti-ferromagnetic (x = 0.0, 1.5, 2.0) or weakly ferromagnetic (x = 0.5, 1.0) at 4.2 ≤ T ≤ 7.6 K. The ordered moments lie along [001] when x = 0.0 and in the (001) plane otherwise. The unit cell doubles along [001] when x = 1.5 and 2.0 order anti-ferromagnetically, but the doubling is lost when a first-order metamagnetic transition to weak ferromagnetism occurs on the application of a 10 kOe magnetic field. The ordered moments at 1.6 K for x = 0.0 and 2.0 are 4.61(2) and 2.58(2) μ, respectively; the corresponding effective moments in the paramagnetic phase are 5.91 and 5.36 μ.

Polycrystalline Y 2 CoGe 4 O 12 has been prepared by standard ceramic methods. The crystal structure (space group P4/nbm; a = 9.8465(2), c = 4.92986(9) Å) consists of metal-rich layers separated from each other by Ge 4 O 12 groups comprised of four corner-sharing GeO 4 tetrahedra. Two cation sites lie within the layers; an eight-coordinate site occupied by yttrium and a six-coordinate site occupied by a 1:1 disordered distribution of yttrium and cobalt.Neutron diffraction revealed two-fold disorder on the oxide sublattice; this has been elucidated using Co K-edge EXAFS spectroscopy. The availability of two sites allows each oxide ion to accommodate the coordination preferences of its single Co/Y neighbour; the GeO 4 tetrahedra distort to absorb any consequent strain. The octahedron of anions around each Co 2+ cation shows a pseudo-tetragonal distortion with a strain (Co -O) eq -(Co -O) ax /(Co -O) eq = -0.173. This results in an unusually large effective magnetic moment of 6.05 µ B per Co 2+ cation.