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This article presents the successful synthesis and characterization of a novel high dielectric constant ceramic system with near-zero temperature coefficient for microwave applications. The system, based on the 5CaO–10SrO–BaO–9Li2O–10Sm2O3–2Nd2O3–63TiO2 composition, was developed through a systematic modification of the non-stoichiometric CaO–Li2O–Sm2O3–Nd2O3–TiO2 (16:9:10:2:63) ceramic system using the conventional solid-state method. The initial focus of the study was on the effect of Sr substitution for Ca. By varying the Sr content from 1 to 11 mol% and sintering at temperatures ranging from 1120 to 1240 °C, it was observed that increasing Sr substitution led to a higher dielectric constant (εr), while the quality factor multiplied by the resonant frequency (Q × f) decreased, and the temperature coefficient of resonant frequency (τf) increased. Notably, at 1180 °C, the optimized composition with 11 mol% Sr substitution (CaO–SrO–Li2O–Sm2O3–Nd2O3–TiO2 = 5: 11: 9: 10: 2: 63) achieved a dielectric constant of 140 and an acceptable Q × f value of 1,100 GHz. However, the τf value was measured as 49.7 ppm/°C, highlighting the need for further optimization for practical applications. To address the issue of the relatively high τf, 1 mol% of BaO was partially substituted for SrO. This substitution resulted in the formation of a Ba-substituted CSBLSNT phase, which successfully improved the τf to near-zero while maintaining a moderate εr. The optimized composition, with a molar ratio of 5: 10: 1: 9: 10:2: 63 for CaO–SrO–BaO–Li2O–Sm2O3–Nd2O3–TiO2, was sintered at 1180 °C for 4 h. The resulting ceramic exhibited excellent dielectric properties: εr = 132, Q × f = 1,200 GHz, τf = 5.3 ppm/°C. The combination of a high dielectric constant and near-zero τf value makes this ceramic system highly promising for the fabrication of smaller, more thermally stable microwave components. [ABSTRACT FROM AUTHOR]

Sol–gel thin films of amorphous LaNbOx (LNO) were prepared to study the bipolar resistive switching (BRS) properties of Metal/LNO/ITO devices. We investigated the influences of film thickness, top electrode, annealing temperature, post-metal annealing (PMA), and bilayer structure on the resistive switching (RS) characteristics. In comparison to the as-deposited LNO thin film devices, the PMA-treated devices demonstrated better RS characteristics, with lower set/reset voltages (VSet/VReset = − 2.26V/0.9V), longer switching cycles (2466 cycles), and a > 101 Ron/Roff ratio. Furthermore, at 85 °C, the retention time exceeded 104 s, similar to the retention time at room temperature, indicating that random access memory (RRAM) may effectively function over 10 years. The improvement in RS characteristics can be attributed to the formation of an AlOx layer between the upper electrode and the insulating layer after PMA treatment, which increases the oxygen vacancy content and facilitates Al ion diffusion. The addition of a bilayer of Al was implemented to increase the thickness of AlOx, thereby improving the Ron/Roff ratio. However, this addition also degrades the RS properties of the device. Furthermore, the space charge-limited current (SCLC) conduction mechanism dominates in the high resistance state (HRS), while ohmic conduction prevails in the low resistance state (LRS) of the devices. [ABSTRACT FROM AUTHOR]

The structures and microwave dielectric properties of Na5−xAgxTb(MoO4)4 ceramics were explored. Single Na5Tb(MoO4)4 phased solid solutions were obtained for specimens with x values ranging from 0 to 0.07, with a small amount of Mo-rich second phase detected at x = 0.09. Although the solid solution range is very limited, the advantage of silver substitution is that it lowers the sintering temperature, increases the densification, and enhances the dielectric properties of the ceramics. The P–V–L bond theory was employed to analyze the correlations between the chemical bond parameters and microwave dielectric properties, which were predominantly influenced by the ionicity and lattice energy of the Tb–O bond. The Na3.93Ag0.07Tb(MoO4)4 compound sintered at 530 °C exhibited excellent microwave dielectric properties (εr = 8.5, Q × f = 54,000 GHz and τf = − 24 ppm/°C), which are very promising for microwave and millimeter wave applications. [ABSTRACT FROM AUTHOR]

Climate change poses a significant threat to humanity. Achieving net-zero emissions is a key goal in many countries. Among various energy resources, solar power generation is one of the prominent renewable energy sources. Previous studies have demonstrated that post-processing techniques such as bias correction can enhance the accuracy of solar power forecasting based on numerical weather prediction (NWP) models. To improve the post-processing technique, this study proposes a new day-ahead forecasting framework that integrates weather research and forecasting solar (WRF-Solar) irradiances and the total solar power generation measurements for five cities in northern, central, and southern Taiwan. The WRF-Solar irradiances generated by the Taiwan Central Weather Bureau (CWB) were first subjected to bias correction using the decaying average (DA) method. Then, the effectiveness of this correction method was verified, which led to an improvement of 22% in the forecasting capability from the WRF-Solar model. Subsequently, the WRF-Solar irradiances after bias correction using the DA method were utilized as inputs into the transformer model to predict the day-ahead total solar power generation. The experimental results demonstrate that the application of bias-corrected WRF-Solar irradiances enhances the accuracy of day-ahead solar power forecasts by 15% compared with experiments conducted without bias correction. These findings highlight the necessity of correcting numerical weather predictions to improve the accuracy of solar power forecasts. [ABSTRACT FROM AUTHOR]

Novel K2Co2(MoO4)3 microwave dielectric materials were prepared and investigated for the first time. The effects of substituting Ag+ for K+ and Zn2+ for Co2+ on the ceramic structure, sintering temperature, surface microstructure, and microwave dielectric properties were studied. The X-ray diffraction results showed that the samples had a monoclinic crystal structure and belonged to the P121/c1 (14) space group, with a single-phase composition of K2Co2(MoO4)3. The pure phase K2Co2(MoO4)3 ceramic achieved a Q × f = 42,300 GHz, an εr = 7.31, and a τf = − 81.3 ppm/°C at a sintering temperature of 630 °C. Partial substitution in the specimen can effectively enhance its densification and reduce the dielectric loss, particularly at the K-site. This improvement is primarily attributed to the more significant variation in the cell volume of the ceramics. The K2Co1.9Zn0.1(MoO4)3 specimen with minute substitution achieved Q × f = 57,300 GHz, εr = 7.82 and τf = − 69 ppm/°C at 630 °C, while the K1.86Ag0.14Co2(MoO4)3 specimen showed Q × f = 61,200 GHz, εr = 8.73 and τf = − 68 ppm/°C at 540 °C. The research also exhibited that the material had outstanding chemical compatibility with aluminum electrodes during co-firing. Based on the results, these ceramics show potential as attractive candidates for ULTCC applications, such as an 8 × 8 dual-polarization antenna array used in the millimeter-wave region for 5G/6G systems. [ABSTRACT FROM AUTHOR]