High-quality LaxCeyPr1-x-yB6 single crystal with excellent thermionic emission properties grown by optical floating zone melting method

Wang, Yan; Zhang, Jiuxing; Yang, Xinyu; Zhu, Zicheng; Zhao, Jingjing; Xu, Bin; Li, Zhi

doi:10.1016/j.jallcom.2018.08.046

Cited by 16 publications

(14 citation statements)

References 23 publications

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“…This right deviation can be ascribed to the phenomenon of lanthanide contraction, that is, r (La 3+ ) > r (Ce 3+ ) > r (Pr 3+ ), as described in Ref. [9].…”

Section: Resultsmentioning

confidence: 80%

“…The flexure strength was measured at room temperature by a three-point bending tester (IBTC-5000, CARE Measurement & Control, China) with a span of 12 mm and a loading rate of 0.5 mm/min, and the size of tested samples was about 3 mm × 4 mm × 20 mm. Thermionic emission examination of the as-sintered sample was carried out by an electron emission measurement system (QX-350, Qixing Vacuum, China) at a vacuum of better than 5 × 10 −5 Pa. For the purpose of comparison with our previous works, 9,10,15 the rectangular tested sample of 1 × 1 × 3 mm 3 in size was carbon covered, as shown in Figure 1, in which only a 1 × 1 mm 2 surface could emit electron effectively. Ultraviolet photoelectron spectroscopy (UPS) was performed for the determination of work function of La 0.6 Ce 0.3 Pr 0.1 B 6 -ZrB 2 by PHI 5000 VersaProbe III with He I source (21.22 eV) under an applied negative bias of 9.0 V. Small samples of dimension 3 × 3 × 3 mm 3 cut by electrical discharge machining were used for non-isothermal oxidation, that is, thermogravimetric (TG) and isothermal oxidation studies by a TGA apparatus (TGA 8000, PE, America) in an air flow of rate of 50 ml/min.…”

Section: Methodsmentioning

confidence: 99%

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Spark plasma sintering of polycrystalline La_0.6Ce_0.3Pr_0.1B₆–ZrB₂ composites

et al. 2022

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This paper has studied the densification, microstructure, and properties of polycrystalline La 0.6 Ce 0.3 Pr 0.1 B 6 -ZrB 2 composites prepared by spark plasma sintering (SPS). The highest relative density of 98.7% is obtained at the SPS condition of axial mechanical pressure 50 MPa, sintering temperature 1900 • C and holding time 5 min. The Vickers hardness decreases linearly from the maximum value of 21.49 GPa to the value of 8.24 GPa with the tested temperature increased from room temperature to 1000 • C. The effects of crack deflection and bridging have resulted in the fracture toughness of 4.56 MPa m 1/2 of dense polycrystalline La 0.6 Ce 0.3 Pr 0.1 B 6 -ZrB 2 composite. The J 1kV of 7.02 A/cm 2 obtained at 1600 • C, the work function of 2.743 eV determined by ultraviolet photoelectron spectroscopy, and the good oxidation resistance below 1100 • C in air have revealed that the dense polycrystalline La 0.6 Ce 0.3 Pr 0.1 B 6 -ZrB 2 composite has a good potential to be a promising hot cathode material.

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“…This right deviation can be ascribed to the phenomenon of lanthanide contraction, that is, r (La 3+ ) > r (Ce 3+ ) > r (Pr 3+ ), as described in Ref. [9].…”

Section: Resultsmentioning

confidence: 80%

Section: Methodsmentioning

confidence: 99%

Spark plasma sintering of polycrystalline La_0.6Ce_0.3Pr_0.1B₆–ZrB₂ composites

et al. 2022

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“…Full‐width at half‐maximum (FWHM) is an effective evaluation to confirm the integrality of crystal structure . The crystal integrality is higher due to the smaller FWHM.…”

Section: Resultsmentioning

confidence: 99%

“…The enhancement of emission current density should be attributed to the less evaporation in the zone‐melting process due to the high density of feed rod, which results in a stable B/Pr atomic ratio in PrB 6 single crystal. Furthermore, another major reason is that the lower work function of PrB 6 single crystal using a high‐density feed rod, which is caused by its higher crystal quality, contributes to improving the emission properties. The work function ( Φ ) of the as‐grown PrB 6 single crystals can be calculated by the Richardson–Dushman formula:

Φ = K T \ln (\frac{A T^{2}}{J_{0}})

, where K is Boltzmann constant ( K = 8.617 × 10 −5 eV K −1 ), T is the cathode temperature, A = 120.4 A cm −2 K −2 is the emission constant, J 0 is the zero field emission current density and can be obtained by the Schottky effect:

\lg J = \lg J_{0} + 0.191 U^{0.5} false(\frac{α^{0.5}}{T} false)

, where α is the experimental constant related to the cathode structure.…”

Section: Resultsmentioning

confidence: 99%

Density of Feed Rod Dependence of the PrB₆ Single Crystal Grown by the Optical Floating Zone Technique

Wang

Zhao

Yang

et al. 2019

Crystal Research and Technology

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Rare-earth hexaboride single crystals praseodymium hexaboride (PrB 6 ) are successfully grown by the optical floating zone technique using the feed rods with different densities sintered by spark plasma sintering (SPS). Single crystal X-ray diffraction and transmission electron microscopy analysis have found that the as-grown PrB 6 adopts a single crystalline structure which has a primitive cubic structure, and has grown along the <100> direction. Particular attentions are given to the effect of density of feed rod on the crystal quality and thermionic emission performance of PrB 6 single crystals. The result of X-ray rocking curve indicates that the quality of the as-grown single crystals get better with increase in the density of feed rod, and an ultralow full-width at half-maximum of 0.066°, confirming the good crystal integrality, is resulted from the single crystal using the feed rod with relative density of 97.17%. Similarly, the result of thermionic emission shows that the PrB 6 single crystal grown here using a high-density feed rod has a large current density. The density of feed rod plays an important role in PrB 6 single crystal growth by the optical floating zone technique.

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“…where k is the Boltzmann constant, k = 8.62 × 10 −5 eV K −1 , A = 120.4 A cm −2 K −2 , and J 0 is the zero-field current density and obtained from the Schottky equation: 34 Lg J = Lg J 0 + 0.192U 0.5 T −1 (4) According to eqn (4), J 0 can be obtained at U 0.5 = 0, as shown in Fig. 10b.…”

Section: Characterization Of the Single Crystalmentioning

confidence: 99%