Yuqiang Zhao

Effectively enhanced oxygen sensitivity of individual ZnO tetrapod sensor by water preadsorption

In this letter, individual ZnO tetrapod was designed as a multiterminal sensor. The gas-sensing properties of water and oxygen of the device have been investigated. We found that if water was preadsorbed on the device, the sensitivity of oxygen can be effectively enhanced; meanwhile, the response time can also be remarkably shortened. The mechanism of these phenomena, we propose, is the adsorption competition of the two kinds of molecules. Our results show that the preadsorption of appropriate gas can enhance the performance of the sensors, which is helpful for sensor designing.

Enhanced Negative Thermal Expansion in La1–xPrxFe10.7Co0.8Si1.5 Compounds by Doping the Magnetic Rare-Earth Element Praseodymium

Experiments have been performed to enhance negative thermal expansion (NTE) in the La(Fe,Co,Si)13-based compounds by optimizing the chemical composition, i.e., proper substitution of La by magnetic element Pr. It is found that increasing the absolute value of the average coefficient of thermal expansion (CTE) in the NTE temperature region (200-300 K) attributes to enhancement of the spontaneous magnetization and its growth rate with increasing Pr content. Typically, the average CTE of La(1-x)Pr(x)Fe10.7Co0.8Si1.5 with x = 0.5 reaches as large as -38.5 × 10(-6) K(-1) between 200 and 300 K (ΔT = 100 K), which is 18.5% larger than that of x = 0. The present results highlight the potential applications of La(Fe,Co,Si)13-based compounds with a larger NTE coefficient.

Broad negative thermal expansion operation-temperature window in antiperovskite manganese nitride with small crystallites

Using spark plasma sintering (SPS), Mn3Cu0.6Ge0.4N crystallites have been fabricated with different crystallite sizes, and their magnetic properties and thermal behaviors were systemically investigated. With decreasing crystallite size, the magnetic transition becomes increasingly slow, accompanied by broadening of the negative thermal expansion (NTE) operation-temperature window. The NTE operation-temperature window for the 12-nm crystallite sample reaches at 140 K, which is about 75% larger than that of the 74-nm crystallite sample. The magnetic properties and NTE operation-temperature window can be tuned by varying the crystallite size. This discovery will promote an even wider range of practical applications in precision devices.

Broad Negative Thermal Expansion Operation-Temperature Window Achieved by Adjusting Fe–Fe Magnetic Exchange Coupling in La(Fe,Si)13 Compounds

Cubic La(Fe,Si)13-based compounds have been recently developed as promising negative thermal expansion(NTE) materials, but the narrow NTE operation-temperature window(∼110 K) restricts their actual applications. In this work, we demonstrate that the NTE operation-temperature window of LaFe(13-x)Si(x) can be significantly broadened by adjusting Fe-Fe magnetic exchange coupling as x ranges from 2.8 to 3.1. In particular, the NTE operation-temperature window of LaFe10.1Si2.9 is extended to 220 K. More attractively, the coefficients of thermal expansion of LaFe10.0Si3.0 and LaFe9.9Si3.1 are homogeneous in the NTE operation-temperature range of about 200 K, which is much valuable for the stability of fabricating devices. The further experimental characterizations combined with first-principles studies reveal that the tetragonal phase is gradually introduced into the cubic phase as the Si content increases, hence modifies the Fe-Fe interatomic distance. The reduction of the overall Fe-Fe magnetic exchange interactions contributes to the broadness of NTE operation-temperature window for LaFe(13-x)Si(x).

Giant isotropic magnetostriction in NaZn13-type LaFe13−xAlx compounds

The unusual low-temperature magnetostrictive property is of fundamental interest due to significant applications in rapidly developing cryogenic engineering. Here, we report a giant isotropic magnetostriction (λ = 1500 ppm, ω = 4500 ppm) over a wide temperature range (∼210 K), and the saturated volume magnetostriction can be up to 8400 ppm in cubic NaZn13-type LaFe13−xAlx compounds by optimizing the chemical composition. The large magnetostrictive effect often occurs in ferromagnetic materials. However, we discovered that the magnetic-field-induced volume expansion originates from the change of lattice parameters across the first-order transition from the low-volume antiferromagnetic ground state to the high-volume ferromagnetic state. Moreover, the magnetostrictive materials show an excellent zero thermal expansion (ZTE) property, which guarantees their reliability and stability operating at various temperatures. The present study suggests potential applications of La(Fe, Al)13-based compounds as ZTE and...

Thermal Expansion and Magnetostriction Measurements at Cryogenic Temperature Using the Strain Gauge Method

Thermal expansion and magnetostriction, the strain responses of a material to temperature and a magnetic field, especially properties at low temperature, are extremely useful to study electronic and phononic properties, phase transitions, quantum criticality, and other interesting phenomena in cryogenic engineering and materials science. However, traditional dilatometers cannot provide magnetic field and ultra-low temperature (<77 K) environment easily. This paper describes the design and test results of thermal expansion and magnetostriction at cryogenic temperature using the strain gauge method based on a Physical Properties Measurements System (PPMS). The interfacing software and automation were developed using LabVIEW. The sample temperature range can be tuned continuously between 1.8 and 400 K. With this PPMS-aided measuring system, we can observe temperature and magnetic field dependence of the linear thermal expansion of different solid materials easily and accurately.

Negative thermal expansion in cubic and tetragonal structure coexisted La(Fe,Si)13hydride

In this research, the cubic and tetragonal crystal structure coexisted LaFe10.0Si3.0 compound and its hydride have been prepared by the arc-melting method and the novel electrolytic hydriding. Furthermore, the crystal structure, magneticand negative thermal expansion (NTE) properties of LaFe10.0Si3.0 and its hydride were investigated by the X-ray diffraction (XRD) and physical property measurement system (PPMS). Intriguingly, the NTE operation-temperature window of LaFe10.0Si3.0 has been broadened significantly after introducing interstitial hydrogen atoms. The further magnetic characterizations combined with theoretical analysis reveal that the increase of ferromagnetic to paramagnetic transition temperature due to stronger Fe-Fe magnetic exchange interactions contribute to the broad NTE operation-temperature window in the LaFe10.0Si3.0 hydride.