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A series of graphene-S 0.05 Co 4 Sb 11.6 Te 0.4 (C x -S 0.05 Co 4 Sb 11.6 Te 0.4) composite polycrystalline skutterudite materials with graphene stoichiometric ratio of x = 0, 0.05, 0.10, 0.20 have been successfully prepared by high pressure and high temperature (HPHT) technology. Graphene is a two-dimensional material with large carrier mobility and large specific surface area. Through microscopic observation, it is found that graphene is attached to the grains in the sample. At the same time, with the increase of graphene content, grain growth is inhibited. Graphene addition reduces the thermal conductivity of skutterudite by increasing grain boundaries and achieves the purpose of optimizing its thermoelectric properties. At the same time, there are numerous lattice defects and distortions introduced in skutterudite synthesized by HPHT technology. Finally, the samples were synthesized under the conditions of 1.5 GPa and 900 K. The lattice thermal conductivity of the graphene composite sample C x -S 0.05 Co 4 Sb 11.6 Te 0.4 with x = 0.10 reaches a minimum of 0.99 at 773 K, and the zT value of this sample is 1.25 at 773 K, which is greater than pure S 0. 05 Co 4 Sb 11.6 Te 0.4 , its zT value is 1.00 at 773 K. Compared with the method of synthesizing skutterudite under normal pressure, the HPHT technology can dramatically reduce the reaction time from several days to less than 30 min, while forming a high-pressure airtight reaction environment, which can effectively prevent the volatilization and oxidation of samples during the reaction process, thus providing a convenient method for synthesizing thermoelectric materials quickly and efficiently. [ABSTRACT FROM AUTHOR]

The persistent luminescence (PersL) materials suitable for high-temperature environments have attracted extensive attention in recent years. Herein, we have reported a novel long-persistent luminescent material of CaYGaO 4 :Bi3+, with a peak wavelength of 430 nm and a duration of more than 40 min at room temperature at the 0.32 mcd/m2 threshold value after UV irradiation. A series of thermoluminescence measurements reveal that the CaYGaO 4 :Bi3+ phosphor has abundant shallow and deep traps with a wide range of distribution. In addition, we utilize the ion substitution strategy of Sr2+ partially replacing Ca2+ ions to increase the shallow trap concentration, so as to improve the performance of PersL at room temperature. More importantly, we investigate the PersL performance of CaYGaO 4 :Bi3+ phosphor at high-temperature environment. As the result demonstrates, when the ambient temperature is in the high-temperature range (450 K–600 K), the phosphor has more obvious brightness. Finally, we take advantage of the phosphor to carry out a demonstration experiment and obtain a set of temperature-related color conversion images, which unequivocally signifies that the phosphor has broad application prospects in anti-counterfeit fields and emergency indicator marks in high-temperature and harsh environments. The CaYGaO 4 :Bi3+ phosphor with abundant shallow and deep traps, which has excellent persistent luminescence performance in the high-temperature environment. [Display omitted] • A blue-emitting persistent luminescence (PersL) through doping Bi3+ ions was achieved in the CaYGaO 4 matrix. • The partial cation substitution strategy was effective and significantly enhanced the persistent luminescence performance. • The improvement of PersL performance at high temperature is due to the accelerated release of trapped electrons. • The CaYGaO 4 :Bi3+ phosphor has broad application prospects in high-temperature and harsh environments. [ABSTRACT FROM AUTHOR]

SrTiO 3 (STO) is considered a promising high-temperature N-type thermoelectric material. However, its intrinsic insulating properties and high thermal conductivity limit the dimensionless quality factor (zT) due to its simple crystal structure and the existence of light elements. Along these lines, in this work, the optimization of the thermoelectric properties of STO-based materials was achieved by using the high temperature and high pressure (HPHT) method and adjusting the doping ratios of the La and Nb heavy elements. To enhance the doping effect, oxygen vacancies need to be formed within the sample. For this reason, titanium powder was added to the sample. Due to the confined environment induced by the high pressure, which can be attributed to the application of the HPHT method and the strong oxygen trapping ability of Ti at high temperatures, a reducing environment was attained for the samples, the latter, promoted the formation of oxygen vacancies in the synthesized samples, and semiconducting properties were achieved. The thermoelectric properties and microscopic morphology of the synthesized samples with different doping ratios of La and Nb were also thoroughly investigated. Finally, the maximum zT value obtained for the samples was 0.28@973 K. A fast, simple, and effective method for the preparation of oxygen-deficient packet-crystalline oxide materials was developed in this work, which paves the way for significantly improving their thermoelectric properties. [ABSTRACT FROM AUTHOR]

Alginate oligosaccharides (AOS) are known for functions in regulating plant growth and stress resistance. This study investigated the damage on rice leaves caused by acid rain (AR) and high temperature (HT) simultaneously, as well as the alleviating effect of AOS on these stresses. The results show that plant biomass and antioxidant enzyme activities (AEAs) after AR treatment reduced more severely under HT conditions than normal-temperature conditions. Both AR and HT triggered the accumulation of reactive oxygen species (ROS) in rice leaves. The suppressing effects of AR and HT were individual in most cases, except for AEAs. Microscopic analysis showed that pH 2 AR and HT injured leaf epidermis, particularly the bulliform cells, the veins and interveinal regions. Spraying AOS resulted in a slight elevation of biomass, a significant increase in AEAs and a remarkable decline in ROS concentrations under HT conditions with AR. Besides, the chlorophyll a contents of a leaf after pH 2 AR plus AOS treatment under HT conditions remained 66.1% of that after pH 7 treatment under normal-temperature conditions. Moreover, AOS protected the integrity of leaf tissue even after pH 3 treatment. Taken together, the above results suggest that AR and HT inhibited AEAs, led to the accumulation of ROS and damaged rice leaf. However, foliar applying AOS enhanced AEAs, scavenged ROS, and thus alleviated the stress induced by HT and AR. [ABSTRACT FROM AUTHOR]

Bi 2 S 3 is considered a promising n-type thermoelectric (TE) material due to its inherent extremely low thermal conductivity and earth-abundant elements. Herein, we have successfully synthesized a series of Nb-doped Bi 2 S 3 (Bi 2-x Nb x S 3 , x = 0, 0.01, 0.02, 0.03) bulk materials by combining mechanical alloying (MA) method and high pressure and high temperature (HPHT) technology. The enhanced electrical transport properties of the Nb-doped Bi 2 S 3 samples is derived from the collaborative optimization of carrier concentration and effective mass, which indicated that the Nb dopants acted as donors. In addition, differences in the direction of the lattice fringes were observed in the samples, and a large number of lattice distortions and dislocation defects occurred, which significantly reduced the lattice thermal conductivity of the Bi 2 S 3 material. Consequently, a peak zT of 0.22 was achieved for the Bi 1.98 Nb 0.02 S 3 sample at 543 K, which is 120% higher than that of pure Bi 2 S 3. • Nb-doped Bi 2 S 3 samples were fabricated via mechanical alloying method followed by high-pressure and high-temperature. • The carrier concentration, carrier mobility, and effective mass of Bi 2 S 3 can be synergistically optimized via Nb doping. • The high synthetic pressure and Nb-doping introduce defects to enhance phonon scattering. • The maximum zT value for Bi 1.98 Nb 0.02 S 3 reached 0.22 at 543 K. [ABSTRACT FROM AUTHOR]

As an oxide thermoelectric material, the adjustment of oxygen vacancy plays an important role in strontium titanate (SrTiO 3). Traditional synthesis methods typically necessitate post-synthesis reduction annealing to optimize its electrical properties. However, the oxygen vacancy concentration of samples synthesized by this approach may be distributed in a gradient manner. In this study, a high-temperature and high-pressure (HPHT) synthesis treatment was adopted, incorporating titanium powder into the raw material. This novel approach leverages the closed environment created by high pressure and the robust oxygen-trapping capabilities of titanium powder at elevated temperatures. It resulted in enhanced electrical properties in synthesized samples without the need for reduction annealing. Building upon this achievement, we successfully synthesized SrTiO 3 samples doped with lanthanum (La) at different pressures. The sample synthesized at 5GPa demonstrated an optimal zT value of 0.22 at 973 K. This work provides a novel approach to the effective synthesis and improved electrical properties of strontium-based thermoelectric materials. • The grain size and band gaps of SrTiO 3 were effective optimized. • Partial high pressure features of SrTiO 3 have been captured to the ordinary pressure. • The whole synthesis procedure last only for 40 min • Ubiquitous lattice defect engineering was realized in our samples by HPHT. [ABSTRACT FROM AUTHOR]