Elsevier

Journal of Alloys and Compounds

Volume 788, 5 June 2019, Pages 1231-1239
Journal of Alloys and Compounds

Thermo-mechanical properties of fluorite Yb3TaO7 and Yb3NbO7 ceramics with glass-like thermal conductivity

https://doi.org/10.1016/j.jallcom.2019.02.317Get rights and content

Highlights

  • The Yb3TaO7 and Yb3NbO7 are synthesized by solid-state reaction.

  • The relationship between crystal structure and property is determined.

  • The glass-like thermal conductivity of Yb3TaO7 and Yb3NbO7 is reported.

  • The lowest thermal conductivity reaches 1.04 W m−1 K−1.

  • The TECs reaches 10.6 × 10 K−6 at 1200 °C.

Abstract

Fluorite structural Yb3TaO7 and Yb3NbO7 with glass-like thermal conductivity are investigated as candidate thermal insulation materials in this work. The relationship between thermo-mechanical properties and crystal structure of Yb3TaO7 and Yb3NbO7 ceramics has been determined. The crystal structure is characterized via X-ray diffraction (XRD), Raman spectrum and X-ray photoelectron spectroscopy (XPS), and the microstructure is observed by scanning electron microscope (SEM). Yb3TaO7 and Yb3NbO7 exhibit the ultralow glass-like thermal conductivity (1.04 W m−1 K−1), which derives from the long-range disordered atomic arrangement. The weaker bonding strength leads to higher TECs, lower thermal conductivity and Young' modulus of Yb3NbO7, compared with Yb3TaO7. Besides, the outstanding high-temperature phase stability, high hardness and fracture toughness of Yb3TaO7 and Yb3NbO7 imply that they are promising high-temperature thermal insulation ceramics.

Introduction

Diverse fundamental applications relate to the release and absorption of energy. Management of ensuring thermal flow relates to the selection of materials with appropriate thermal conductivity. For example, to improve the thermal insulation performance of thermal barrier coatings (TBCs), low thermal conductivity is demanded [[1], [2], [3], [4], [5]]. Besides, low thermal conductivity is required for thermoelectric materials to optimize the thermoelectric figure of merit [[6], [7], [8]]. In contrary, many electronic devices require high thermal conductivity to facilitate heat extraction, such as integrated circuits. To adjust the thermal conductivity of materials, much effort has been carried out to comprehend the thermal conduction mechanisms and regulate the thermal conductivity. TBCs are one of the most investigated materials as its importance to gas turbines and aero engines [[9], [10], [11]]. The primary functions of TBCs are to provide thermal insulation and improve the gas efficiency [[12], [13], [14]]. Therefore, researchers have dedicated to decreasing the thermal conductivity of TBCs. In insulation materials, the thermal conduction is dominated by lattice vibration, i.e., phonons, and the thermal conductivity (k) is [15]:k=1/3CVVMlWhere CV is the heat capacity, VM is the mean acoustic velocity and l is the phonon mean free path. VM relates to the interatomic interaction, and the heat capacity reaches 3kB per atom at high temperature according to the Dulong-Petit law. Hence, the phonon mean free path decides the thermal conductivity of insulation materials. During the propagation of phonons, the phonon mean free path (l) with certain frequency (f) is reduced by diverse phonon scattering processes [[16], [17], [18]]:1l(f,T)=1l(f,T)i+1l(f,T)d+1lbWhere l(f, T)i is the phonon free path deriving from the intrinsic crystal structure scattering, i.e., the Umklapp phonon scattering process. l(f, T)d is the phonon free path originating from point defects scattering, such as oxygen vacancy and the losing interatomic linkages. lb is the phonon free path rooting in the grain boundary scattering [[16], [17], [18]]. To reduce the thermal conductivity, the phonon scattering strength is reinforced to decrease the phonon mean free path. Usually, the Umklapp phonon scattering strength increases with the increasing temperature, which leads to the typical k ∝ T−1 relationship. Oxygen vacancy is effective phonon scattering center; the thermal conductivity of ZrO2 is reduced by the Y2O3 substitution due to the introduction of oxygen vacancy (YSZ) [19,20]. The point effect phonon scattering strength is temperature independent, and it relates to the concentration. As for the grain boundary phonon scattering, the scattering strength decreases with the increasing temperature when the grain size reaches nanometer scale [21,22]. Nevertheless, the grain boundary phonon scattering strength can be omitted when the grain size is micro scale [21,22]. Thus, the thermal conductivity of insulation materials primarily relies on the complexity of crystal structure and point defect concentration.

D. G. Cahill and M. Beekman have summarized the characteristic crystal structures of materials with glass-like thermal conductivity [23]. The crystal structures include NaCl-type (AB), fluorite/anti-fluorite (AB2/A2B), filled-skutterudite (AB4C12), clathrate-I (A8B16C30), Zn4Sb3, WSe2, and Cu3SbSe3 [23]. Ascribed to the differences of crystal structures, the main phonon scattering mechanisms caused glass-like thermal conductivity are different. The glass-like thermal conductivity of some materials has been reported, for example, (La5/6Yb1/6)2Zr2O7 and Dy3TaO7 ceramics [24,25]. The thermal conductivity of RE3TaO7 with ordered crystal structure has been reported, and different crystal structures result in different thermal conductivity [[25], [26], [27]]. However, the thermal conductivity of RE3TaO7 with disordered fluorite crystal structure is not known yet. Yb3TaO7 and Yb3NbO7 may exhibit glass-like thermal conductivity based on Ref [23], and they are worthy to be investigated as TBCs.

In this work, Yb3TaO7 and Yb3NbO7 were synthesized via solid-state reaction. The crystal structure was characterized by XRD, XPS and Raman spectrums. The microstructure was detected via SEM. The thermo-mechanical properties including thermal conductivity, TECs, phase stability, Vickers hardness, fracture toughness and elastic modulus were investigated systematically. It is proposed that Yb3TaO7 and Yb3NbO7 are promising thermal insulation materials due to the excellent thermo-mechanical properties.

Section snippets

Specimen preparation

The compact Yb3TaO7 and Yb3NbO7 specimens were synthesized via solid-state reaction. The feed stocks were Yb2O3 (purity≧99.9%, 2–20 μm), Ta2O5 (purity≧99.9%, 1–3 μm), Nb2O5 (purity≧99.9%, 5–10 μm) powders and anhydrous ethanol (purity≧99.9%) from aladdin Chem. Co. Shanghai, China. The raw powders were mixed by mole ratio and then ball-milled (6 h, 300 r/min) with anhydrous ethanol. The solution was transferred to a beaker and kept at 68 °C for 12 h to remove anhydrous ethanol. The resulting

Phase structure

The experiment Yb3TaO7 and Yb3NbO7 XRD patterns are consistent with PDF#24-1414 and PDF#24-1130, respectively. Fig. 1(a) shows that the XRD peaks of Yb3TaO7 agree well with that of PDF#24-1414. Both Yb3TaO7 and Yb3NbO7 ceramics are disordered cubic fluorite phase according to the standard PDF cards. As Ta5+ and Nb5+ ions exhibit the equal ionic radius (0.064 nm), no obvious XRD peak shifting is observed in Fig. 1(a). The unit cell volume of Yb3TaO7 and Yb3NbO7 is similar, which is 140 Å3 and

Conclusion

Compact disordered fluorite Yb3TaO7 and Yb3NbO7 specimens are successfully synthesized via solid-state reaction. The surface microstructure of Yb3TaO7 and Yb3NbO7 is similar due to the same sintering condition, and little pores are observed. The band gap of Yb3TaO7 and Yb3NbO7 is 4.66 and 4.08 eV, respectively, indicating that they are insulating materials and heat is transmitted via phonons. The Vickers hardness (9.8 GPa), fracture toughness (1.7 MPa m1/2) and Young's modulus (208.9 GPa) of Yb3

Acknowledgements

This research is under the support of the Natural Science Foundation of China (No. 51762028) and Materials Genome Engineering of Rare and Precious Metal of Yunnan (No.2018ZE019).

References (49)

  • A. Chesnaud et al.

    High-temperature anion and proton conduction in RE3NbO7 (RE=La, Gd, Y, Yb, Lu) compounds

    J. Eur. Ceram. Soc.

    (2015)
  • R.G. Wang et al.

    Properties and microstructure of machinable of Al2O3/LaPO4 ceramic composites

    J. Ceram. Int.

    (2003)
  • O.L. Anderson

    A simplified method for calculating the Debye temperature from elastic constants

    J. Phys. Solid State

    (1963)
  • N.P. Padture et al.

    Thermal barrier coatings for gas-turbine engine applications

    Science

    (2002)
  • L. Chen et al.

    Epitaxial growth and cracking of highly tough 7YSZ splats by thermal spray technology

    J. Adv. Ceram

    (2018)
  • X.Q. Cao et al.

    Lanthanum-cerium as a thermal-barrier-coating material for high-temperature applications

    Adv. Mater.

    (2003)
  • D.R. Clarke et al.

    Materials design for the next generation thermal barrier coatings

    Annu. Rev. Mater. Res.

    (2003)
  • L.D. Zhao et al.

    Ultrahigh power factor and thermoelectric performance in hole-doped single-crystal SnSe

    Science

    (2016)
  • H.L. Liu et al.

    Copper ion liquid-like thermoelectrics

    Nat. Mater.

    (2012)
  • C.L. Wan et al.

    Ultralow thermal conductivity in highly anion-defective aluminates

    Phys. Rev. Lett.

    (2008)
  • A.M. Limarga et al.

    Low thermal conductivity without oxygen vacancies in equimolar YO1.5+TaO2.5- and YbO1.5+TaO2.5-stabilized tetragonal zirconia ceramics

    Acta Mater.

    (2010)
  • W.W. Zhang et al.

    Comprehensive damage evaluation of localized spallation of thermal barrier coatings

    J. Adv. Ceram.

    (2017)
  • L. Chen et al.

    Potential thermal barrier coating materials: RE3NbO7 (RE=La, Nd, Sm, Eu, Gd, Dy) ceramics

    J. Am. Ceram. Soc.

    (2018)
  • C. Kittle

    Introduction to Solid State Physics

    (1996)
  • Cited by (37)

    • Novel (Sm<inf>0.2</inf>Lu<inf>0.2</inf>Yb<inf>0.2</inf>Y<inf>0.2</inf>Dy<inf>0.2</inf>)<inf>3</inf>TaO<inf>7</inf> high-entropy ceramic for thermal barrier coatings

      2023, Ceramics International
      Citation Excerpt :

      The lattice parameter calculated from Fig. 6 is approximately 5.267 Å, which is in the same order with that of fluorite-type (Nd1–xGdx)2(Ce1–xZrx)2O7 oxides [29]. As shown in Fig. 7, there are only two widened vibrational bands at approximately 394 and 785 cm−1 in the Raman spectra of the synthesized nano-powders and bulk sample, respectively, which are consistent with those of Lu3TaO7 [18] and Yb3TaO7 [26]. The Raman spectra in Fig. 7 also indicate a typical fluorite-type lattice, which agrees well with the XRD result.

    View all citing articles on Scopus
    View full text