The controllable isotropic thermal expansion with a broad coefficient of thermal expansion (CTE) window is intriguing but remains challenge. Herein we report a cubic MZrF series (M = Ca, Mn, Fe, Co, Ni and Zn), which exhibit controllable thermal expansion over a wide temperature range and with a broader CTE window (-6.69 to +18.23 × 10/K). In particular, an isotropic zero thermal expansion (ZTE) is achieved in ZnZrF, which is one of the rarely documented high-temperature isotropic ZTE compounds. By utilizing temperature-dependent high-energy synchrotron X-ray total scattering diffraction, it is found that the flexibility of metal···F atomic linkages in MZrF plays a critical role in distinct thermal expansions. The flexible metal···F atomic linkages induce negative thermal expansion (NTE) for CaZrF, whereas the stiff ones bring positive thermal expansion (PTE) for NiZrF. Thermal expansion could be transformed from striking negative, to zero, and finally to considerable positive though tuning the flexibility of metal···F atomic linkages by substitution with a series of cations on M sites of MZrF. The present study not only extends the scope of NTE families and rare high-temperature isotropic ZTE compounds but also proposes a new method to design systematically controllable isotropic thermal expansion frameworks from the perspective of atomic linkage flexibility.

No abstract

The negative thermal expansion (NTE) behavior provides us an opportunity to design materials with controllable coefficient of thermal expansion (CTE). In this letter, we report a tunable isotropic thermal expansion in the cubic (Sc1−xZrx)F3+δ over a wide temperature and CTE range (αl = −4.0 to+ 16.8 × 10−6 K−1, 298–648 K). The thermal expansion can be well adjusted from strong negative to zero, and finally to large positive. Intriguingly, isotropic zero thermal expansion (αl = 2.6 × 10−7 K−1, 298–648 K) has been observed in the composition of (Sc0.8Zr0.2)F3+δ. The controllable thermal expansion in (Sc1−xZrx)F3+δ is correlated to the local structural distortion. Interestingly, the ordered magnetic behavior has been found in the zero thermal expansion compound of (Sc0.8Zr0.2)F3+δ at room temperature, which presumably correlates with the unpaired electron of the lower chemical valence of Zr cation. The present study provides a useful reference to control the thermal expansion and explore the multi-functionalization for NTE materials.

Ti-doped Ni 0.68 Fe 2.32 O 4 spinel ferrite samples with nominal composition Ni 0.68À0.8x Ti x Fe 2.32À0.2x O 4 (0 x 0.312) were prepared using conventional ceramic methods. The samples exhibited a single-phase cubic spinel structure. When the doping level had values x > 0.15, a transition temperature, T N , was found, below which the magnetization of the samples decreased with decreasing measurement temperature. This phenomenon indicates that an additional antiferromagnetic structure arises in the traditional spinel phase of ferrites resulted from Ti doping. Therefore, Ti ions appear in the form of Ti 3þ and Ti 2þ cations that have magnetic moments, rather than as Ti 4þ cations without magnetic moment as assumed by many researchers. The dependence of the magnetic moments on the Ti doping level x at 10 K was fitted successfully using our quantum-mechanical potential barrier model proposed earlier. In the fitting process, we assumed that the magnetic moments of the Ti cations were opposite to the direction of the Fe and Ni moments. According to the fitted results, the Ti 2þ cations at the [B] sites constitute about 81% of the total Ti content x for all samples, which is close to the content of the Ni 2þ cations at the [B] sites (77%).

Scandium fluoride (ScF) exhibits a pronounced negative thermal expansion (NTE), which can be suppressed and ultimately transformed into an isotropic zero thermal expansion (ZTE) by partially substituting Sc with Fe in (ScFe)F (Fe20). The latter displays a rather small coefficient of thermal expansion of -0.17 × 10/K from 300 to 700 K. Synchrotron X-ray and neutron pair distribution functions confirm that the Sc/Fe-F bond has positive thermal expansion (PTE). Local vibrational dynamics based on extended X-ray absorption fine structure indicates a decreased anisotropy of relative vibration in the Sc/Fe-F bond. Combined analysis proposes a delicate balance between the counteracting effects of the chemical bond PTE and NTE from transverse vibration. The present study extends the scope of isotropic ZTE compounds and, more significantly, provides a complete local vibrational dynamics to shed light on the ZTE mechanism in chemically tailored NTE compounds.

Power system is facing new challenges and opportunities in the environment of the internet of things. Under the circumstance of Internet of things, the transmission congestion management of interruptible load is the important measure to improve system reliability and operating economy. Considering the condition of target selected under different circumstances, this paper proposes a new multi-objective model of transmission congestion management with interruptible load based on brand circuit overload match with interrupt capacity. The multiobject model puts forward three goals, brand circuit overload match with interruptible load, the minimum number of interruptible load nodes and the minimum total interruption of interruptible load. Against other optimization methods can not prioritize to multiple targets and it can easily lead to convergence in the process of solving problems, the paper presents construct evaluation function based on the linear weighted sum to optimize multi-objective linear problem. This method can be sorted prior to multi-objective optimization model. And it has better convergence than other optimization methods in the solution process. Finally, it tests and verifies the correctness of method through the IEEE 30 bus power system. And it successfully applied to grid congestion management in oil.

No abstract

Isotropic zero thermal expansion (ZTE) is rare but intriguing physical property in materials. Here, we report an isotropic ZTE property in a double ReO3‐type compound of MgZrF6, which exhibits a negligible value of coefficient of thermal expansion (αl = −7.94 × 10−7 K−1 (XRD), αl = −4.22 × 10−7 K−1 (dilatometry), 300‐675 K). The ZTE mechanism of MgZrF6 is understood by the joint studies of temperature dependence of crystal structure and lattice dynamics. Interestingly, different magnitudes of atomic displacement parameters (ADPs) for the fluorine atoms in MZrF6 (M = Ca, Ni, Mg) are found. The strong temperature sensitivity of ADPs demonstrates intensive transverse thermal vibration of fluorine atoms, which contributes essentially to the negative thermal expansion of CaZrF6. By contrast, for NiZrF6 with positive thermal expansion, the temperature response of ADPs is weak. Moderate transverse thermal vibration takes place in MgZrF6, and ZTE appears. Furthermore, lattice dynamics of MgZrF6 is studied by temperature‐dependent Raman spectroscopy, which reveals the ZTE mechanism. In particular, the F2g and Ag modes, corresponding to the bending and stretching vibrations of fluorine atoms, respectively, neither soften nor harden over the whole temperature range, which is correlated with the isotropic ZTE property of MgZrF6.