•The terahertz spectra of TmFeO3 ceramics at various temperatures were measured.•We investigated the spin reorientations of TmFeO3 using terahertz resonances.•An anisotropic energy mechanism was introduced to explain the thermodynamics.•The changes in magnetic properties verified the process of spin reorientations.Continuous transitions Γ4→Γ24→Γ2 have been shown in TmFeO3 orthoferrite. The spin reorientations of TmFeO3 ceramics are investigated using terahertz time domain spectroscopy through ferromagnetic and antiferromagnetic resonances at decreased temperature. An anisotropic energy mechanism is introduced to research the thermodynamics of spin reorientations. It is derived analytically from changes in ferromagnetic resonant frequencies that anisotropic energy Kac decreases and reverses its sign in the vicinity of spin reorientations, and increased antiferromagnetic resonant frequencies originate from increased Kab. Testing M–H (moment–magnetic field) and M–T (moment–temperature) curves, we found changes in macroscopic magnetic properties. Further, thermodynamics and process of spin reorientations are verified.

A second calcination–milling step was introduced in the conventional processing of (K, Na)0.5NbO3 (KNN) ceramics (sintered in air) to further homogenenize the particle size distribution of the pre-sintered powders. The ceramic derived from the powders prepared by the two-step route possesses grains with better uniformity and is more compact. The relative density of the bulk ceramic reached 96.9%. Excellent properties are obtained in as-prepared KNN ceramics with kp=44%, d33=111 pC/N, tanδ=0.85%, ε33T/εo=311, Qm=193, Pr=25.4 μC/cm2, d33⁎=251 pm/V, which are superior to those of the ceramics derived from the powders calcined once as used in the traditional processing. These results indicate that twice-calcination–milling route is shown to be a facile and effective way to simultaneously improve the piezoelectric and ferroelectric properties of KNN ceramics without sintering aids.

Temperature tunable photonic crystals were fabricated based on liquid-infiltrated inverse opal films. The photonic band gaps were investigated at different temperatures by reflection spectra. The results show that the photonic band gap can be tuned continuously by temperature change. In this work, the band gap was blue-shifted from 558 nm to 542 nm with increasing temperature from 28 °C to 48 °C. It will provide a new method of studying the modulation near edge effect of the photonic band gap.Highlights► Tunable photonic crystals were prepared based on solvent-infiltrated SiO2 inverse opal films. ► The photonic band gap was tuned continuously by controlling the temperature. ► The shift will provide a method to study the effects of different positions in photonic band gap.

The influence of iterative heat treatment of impregnated aqueous Mn(NO3)2 solution on the microstructure of the produced MnO2 has been investigated in the fabrication process for niobium suboxide capacitors. We separate the whole process into two stages: At the early stage of impregnations in Mn(NO3)2 solution (with specific density less than 1.35 g/cm3), the produced MnO2 grains with equiaxed nanocrystalline morphology are mainly located in the inner space and pores, avoiding the performance deterioration due to the electrical conductivity anisotropy of columnar texture in NbO capacitors. For impregnation in Mn(NO3)2 solutions with specific density greater than 1.35 g/cm3, MnO2 grains in the inner space and pores continue to grow and present a hexagonal pyramid shape. At this stage, MnO2 starts to be produced on the outer surface of pellets and exhibits a cluster morphology that consists of MnO2 grains with size between 30 nm and 80 nm. The electrical performance of NbO capacitors has been optimized by adjusting the impregnation times and sequence. By alternately impregnating in Mn(NO3)2 solutions with specific densities of 1.23 g/cm3 and 1.35 g/cm3, MnO2 grains are better combined and the internal space of the pellets is fully filled. Impregnation in Mn(NO3)2 solutions with low specific densities (1.10 g/cm3 and 1.23 g/cm3) in dry atmosphere produces a denser MnO2 layer in the internal space, leading to improved capacitor performance.