David P. Cann

Barium titanate (BaTiO ₃ , BT) is widely used in a multitude of dielectric applications, including capacitors, sensors, and energy storage devices. Co-doping in BT has a dramatic influence on the electrical properties, which can be attributed to the crossover from the ferroelectric state to the relaxor state. The relaxor state is triggered by structural disorder, leading to localized fields that interfere with long-range polar order for various cation substitutions and quantities. Here, we investigate the effect of co-doping in BT with rare-earth elements (Ho and Ce) using solid-state synthesis to establish the dopant-property relationship. Structural characterization via X-ray diffraction (XRD) confirmed that all co-doped compositions have a phase-pure, pseudo-cubic perovskite phase. Meanwhile, temperature-dependent dielectric measurements showed that the system exhibited a diffuse phase transition along with a high dielectric constant ([ ]) and a low dielectric loss ([ ]) at the temperature ([ ]C). With an increase in dopant concentration, a maximum diffusivity (±15% of permittivity consistent between 44–77 ^∘ C) was observed at a composition with 5[ ]mol.% Ho and 5[ ]mol.% Ce in BT. The compounded effect of rare-earth element substitution along with the introduction of Ti vacancies causes a transition to relaxor behavior along with a high dielectric constant, comparable to pure BT. This result represents a significant improvement as compared to prior studies on BT or RE-doped-BT ceramics, which show that the compositional modifications to induce relaxor behavior typically suppress the dielectric constant.

Tellurium oxides of the ATeO₃ form typically do not crystallize in perovskite structures. Here, we show that perovskite-like ATeO₃ (A = Ca, Sr, Ba) thin films can be grown on perovskite single-crystal substrates via epitaxial stabilization. These films are stable with high optical bandgaps, low dielectric losses, and a high electric breakdown strength. Hysteretic dielectric behavior found in SrTeO₃ and BaTeO₃ strongly suggests the presence of antiferroelectricity and ferroelectricity, respectively. These properties make perovskite tellurium oxides possibly appealing candidates for thin film coating or insulator materials in advanced microelectronics. Tellurium oxides constitute a largely unexplored class of materials that might show new and interesting functionalities in epitaxial thin-films. Our work encourages new work within this field.

High quality data on the high temperature electrical properties of ceramics, particularly oxides, is of great value for material selection, design, and modeling for a broad range of emerging applications. Utilizing the mismatch in the coefficient of thermal expansion between two materials, a purely mechanical method for establishing electrical contact in the van der Pauw geometry to measure the bulk resistivity of ceramic disks at high temperatures is presented. Measurements of a reference material, 20 mol. % Gd-doped cerium oxide, are presented up to 1000 °C. The viability of electrical measurements up to a maximum temperature of 1600 °C is also considered. Measurements are performed using multiple techniques and compared to literature values finding excellent agreement. The approach described in this work enables the van der Pauw method to be applied to many ceramic materials over a wide range of temperatures and environments.

Phase pure perovskite (1-x)Bi_1/2Na_1/2TiO₃ – xBi_1/2K_1/2TiO₃ (BNKT) thin films were successfully prepared via an inverse mixing order chemical solution deposition method and the impact of process conditions on film properties were observed. Process conditions evaluated included crystallization temperature and time, ramp rate, pyrolysis temperature, and cation excess. Properties measured included crystal structure, dielectric constant, dielectric loss, piezoelectric response, and ferroelectric response. A few notable trends were observed. A subtle impact on piezoelectric response was observed in films prepared using different ramp rates: 100 C per second films (d_33,f = 60 ± 5 pm/V at 1 kHz), 75 °C per second films (d_33,f = 55 ± 5 pm/V) and 150 C per second films (d_33,f = 50 ± 5 pm/V). Films prepared using a 75 °C per second ramp rate displayed slightly higher dielectric loss (tan δ = 0.09 at 1 kHz) than films prepared using a 100 °C per second ramp rate (tan δ = 0.07 at 1 kHz) or 150 °C per second ramp rate (tan δ = 0.05 at 1 kHz). Pyrolysis temperatures greater than 350 °C are necessary to burn off organics and maximize film dielectric constant. Dielectric constant increased from 450 ± 50 at 1 kHz to 600 ± 50 at 1 kHz by increasing pyrolysis temperature from 300 to 400 °C. Excess cation amounts (for compositional control) were also evaluated and it was found films with higher amounts of Na and K excess compared to bismuth excess displayed an increase in d_33,f of about 10 pm/V compared to films prepared with equivalent Bi and Na and K excess amounts. Article highlights: Impact of processing conditions on inverse mixing order chemical solution deposited bismuth based thin films. Dielectric, piezoelectric, and ferroelectric properties of thin film bismuth sodium titanate-bismuth potassium titanate thin films. Developing lead-free piezoelectric actuator materials.