Ferroelastic Ceramics Research Articles

Ferroelastic rare‐earth tantalates for multifunctional thermal/environmental barrier coatings: A perspective

AbstractThis perspective outlines the research directions of ferroelastic rare‐earth (RE) tantalates (RETaO4), which have been studied as multifunctional thermal/environmental barrier coatings (T/EBCs) with working temperatures above 1600°C. Ferroelastic RETaO4 ceramics exhibit several distinct features, including the reversible second‐order ferroelastic phase transition, high toughness, low thermal conductivity, low oxygen ion conductivity, and adjustable thermal expansion coefficients. This perspective provides a concise summary of the research progress on tantalate coatings synthesized via air plasma spraying and electron beam physical vapor deposition. The service performance of tantalate coatings is typically evaluated through thermal fatigue and shock measurements. Uncovering the failure mechanisms and understanding influencing factors are key aspects for future studies. In this regard, establishing the synthesis‐structure‐property relationship of RETaO4 coatings is essential. This brief perspective can serve as a guide for future work on RETaO4 coatings and further advancements in their applications across various fields, including aviation engines and gas turbines.

High-entropy ferroelastic (10RE0.1)TaO4 ceramics with oxygen vacancies and improved thermophysical properties

The primary purpose of this work is to optimize the thermophysical properties of rare-earth tantalate ceramics using the high-entropy effect. Here, the high-entropy rare-earth tantalate ceramic (Y0.1Nd0.1Sm0.1Gd0.1Dy0.1Ho0.1Er0.1Tm0.1Yb0.1Lu0.1)TaO4 ((10RE0.1)TaO4) is synthesized successfully. The lattice distortion and oxygen vacancy concentration are characterized firstly in the rare-earth tantalates. Notably, compared with single rare-earth tantalates, the thermal conductivity of (10RE0.1)TaO4 is reduced by 16%–45% at 100 °C and 22%–45% at 800 °C, and it also presents lower phonon thermal conductivity in the entire temperature range from 100 to 1200 °C. The phonon thermal conductivity (1.0–2.2 W m−1 K−1, 100–1200 °C) of (10RE0.1)TaO4 is lower than that of the currently reported high-entropy four-, five- and six-component rare-earth tantalates. This is the result of scattering by the ferroelastic domain, lattice distortion associated with size and mass disorder, and point defects, which target low-, mid- and high-frequency phonons. Furthermore, (10RE0.1)TaO4, as an improved candidate for thermal barrier coatings materials (TBCs), has a higher thermal expansion coefficient (10.5×10−6 K−1 at 1400 °C), lower Young's modulus (123 GPa) and better high-temperature phase stability than that of single rare-earth tantalates.

Ferroelastic tetragonal-monoclinic phase transition and anisotropic thermal expansion of LuNbO4 ceramics

Rare-earth tantalates (RETaO4) and niobates (RENbO4) are widely studied as promising thermal barrier coatings based on the ferroelastic tetragonal-monoclinic (t-m) phase transition. We studied the t-m transition process, anisotropic thermal expansion coefficients (TECs), and the corresponding spontaneous strain of LuNbO4 by powder high-temperature X-ray diffraction. The results proved that the unit cell volume and TECs continuously increased with increasing temperature, and the dominant mechanisms of thermal expansion were proposed. Two different orientation states (S1 and S2) caused by the t-m transition led to formation of the ferroelastic domains, and the corresponding spontaneous strain was determined. The relationship between the t-m transition and spontaneous strain was proposed for further property tailoring. This work provided an in-depth analysis of the ferroelastic t-m phase transition, and it would advance the applications of ferroelastic ceramics.

Evaluating a Critical Resolved Shear Stress Criterion for Domain Nucleation in Ferroelastic Ceramics

The mechanical behavior of single crystal, ferroelastic, tetragonal, ceria-titania-stabilized zirconia is evaluated through uniaxial micro-scale compression experiments. The deformed single crystal micropillars exhibit characteristics of several deformation modes, including twinning (ferroelastic domain nucleation), dislocation plasticity, and microcracking. Following earlier work that revealed how the onset of twinning obeys a critical resolved shear-stress law, much akin to Schmid's law, we test this model and show that it does not hold for the data presented herein. We ascribe this discrepancy to the fact that multiple deformation mechanisms can be active in different micropillars and even in the same micropillars at room temperature, which is revealed by transmission electron microscopy. Whilst little is known about the potential interactions between these mechanisms at such low homologuous temperatures, their coexistence implies that crystal orientation alone is not sufficient to predict ferroelastic domain nucleation behavior in small-scale single crystals.

Thermal and Mechanical Properties Optimization of ABO4 Type EuNbO4 By the B-Site Substitution of Ta

Abstract Ferroelastic ABO4 type RETaO4 and RENbO4 ceramics (where RE stands for rare earth) are being investigated as promising thermal barrier coatings (TBCs), and the mechanical properties of RETaO4 have been found to be better than those of RENbO4. In this work, B-site substitution of tantalum (Ta) is used to optimize the thermal and mechanical properties of EuNbO4 fabricated through a solid-state reaction (SSR). The crystal structure is clarified by means of X-ray diffraction (XRD) and Raman spectroscopy; and the surface microstructure is surveyed via scanning electronic microscope (SEM). The Young’s modulus and the thermal expansion coefficient (TEC) of EuNbO4 are effectively increased; with respective maximum values of 169 GPa and 11.2 × 10−6 K−1 (at 1200 °C). The thermal conductivity is reduced to 1.52 W·K−1·m−1 (at 700 °C), and the thermal radiation resistance is improved. The relationship between the phonon thermal diffusivity and temperature was established in order to determine the intrinsic phonon thermal conductivity by eliminating the thermal radiation effects. The results indicate that the thermal and mechanical properties of EuNbO4 can be effectually optimized via the B-site substitution of Ta, and that this proposed material can be applied as a high-temperature structural ceramic in future.

Tilt strain glass in Sr and Nb co-doped LaAlO3 ceramics

Strain glass, a glassy state of lattice strain, has been found in Ti50-xNi50+x alloys and later in many metallic ferroelastic/martensitic systems, where shear or shuffle serves as a primary order parameter (POP). Another class of non-metallic ferroelastic ceramics are also known to widely exist and commonly possess a polyhedral tilt as the POP. So far, it is unclear whether a “tilt” strain glass exists. Here, we report a finding of a tilt strain glass in La1-xSrxAl0.95Nb0.05O3-δ ceramics. With increasing Sr2+ dopants, the ferroelastic transition from cubic to rhombohedral phases is gradually suppressed. At a critical concentration (xc ∼10%), a strain glass transition emerges, characterized by five sets of evidence: (I) an invariance of average structure; (II) frequency dependence of elastic moduli at a strain glass transition temperature Tg; (III) non-ergodicity; (IV) formation of rhombohedral nanodomains; (V) a gradual increase of tilt angle upon cooling. Surprisingly, the established phase diagram shows an increase of Tg with increasing dopants (a positive correlation), which is different from previous strain glass phase diagrams. The positive and negative correlations can be explained as a balance between two factors of strain glass transition: a global transition factor producing a negative contribution competes with a local field one producing a positive contribution. Our discovery of strain glass in ceramics may also bring novel properties as in metals.

Thermal expansion performance and intrinsic lattice thermal conductivity of ferroelastic RETaO4 ceramics

AbstractFerroelastic RETaO4 ceramics are promising thermal barrier coatings (TBCs) because of their attractive thermomechanical properties. The influence of crystal structure distortion degree on thermomechanical properties of RETaO4 is estimated in this work. The relationship between Young's modulus and TECs is determined. The highest TECs (10.7 × 10−6 K−1, 1200°C) of RETaO4 are detected in ErTaO4 ceramics and are ascribed to its small Young's modulus and low Debye temperature. The intrinsic lattice thermal conductivity (3.94‐1.26 W m−1 K−1, 100‐900°C) of RETaO4 deceases with increasing of temperature due to an elimination in thermal radiation effects. The theoretical minimum thermal conductivity (1.00 W m−1 K−1) of RETaO4 indicates that the experimental value is able to be reduced further. We have delved deeply into the thermomechanical properties of ferroelastic RETaO4 ceramics and have emphasized their high‐temperature applications as TBCs.

Emergent large mechanical damping in ferroelastic-martensitic systems driven by disorder

Disorders and point defects strongly interplay with the phase transition and alter the properties of ferroelastic-martensitic systems. Unusual static and quasistatic behaviors, such as time-dependent phase transitions, are discovered when disorders are introduced. However, the role of disorders on the ferroelastic system in vibrational environments at moderate frequency is rarely known, investigation of which could further shed light on their application as mechanical damping materials. Here we present the emergence of large damping capacity in ferroelastic-martensitic systems [including both the $\mathrm{T}{\mathrm{i}}_{50\ensuremath{-}x}\mathrm{N}{\mathrm{i}}_{50+x}$ alloy and $(\mathrm{C}{\mathrm{a}}_{1\ensuremath{-}x}\mathrm{S}{\mathrm{r}}_{x})\mathrm{Ti}{\mathrm{O}}_{3}$ ceramics] by introducing disorder (i.e., substitutional Ni and Sr, respectively). As the level disorder increases, the damping capacity of both systems raises and eventually reaches a maximum when long-range-ordered martensite tends to vanish. Moreover, near the disorder-induced phase boundary, we observe a large mechanical damping in ferroelastic ceramics $(\mathrm{C}{\mathrm{a}}_{1\ensuremath{-}x}\mathrm{S}{\mathrm{r}}_{x})\mathrm{Ti}{\mathrm{O}}_{3}$ with a figure of merit $\ensuremath{\sim}2\phantom{\rule{0.16em}{0ex}}\mathrm{GP}{\mathrm{a}}^{1/2}$. Microscopic and dynamic investigations indicate that such damping plateau could result from the competing evolution of density and mobility of domain boundaries when disorder is introduced. Our work provides a degree of freedom to develop ferroelastic damping materials and a potential way to tune domain-boundary-mediated functionalities for other ferroic materials.

Synthesis and thermophysics properties of ferroelastic SmNb1-XTaXO4 ceramics

Monoclinic phase SmNb1-XTaXO4 ceramics are synthesized via solid-state reaction. X-ray diffraction and Raman spectra are applied to characterize the crystal structure. The ferroelasticity of SmNb1-XTaXO4 ceramics is confirmed by the domain structure observed via scanning electron microscopy. The band gap of SmNb1-XTaXO4 ceramics ranges from 4.3 to 5.0 eV and they exhibit excellent absorption for UV light. Thermophysics properties including specific heat, thermal diffusivity, thermal conductivity and thermal expansion coefficients of SmNb1-XTaXO4 ceramics are investigated systematically. The result shows that the thermal conductivity of SmNb1-XTaXO4 ceramics is as low as 1.33 W m−1 K−1 (900 °C) and the thermal expansion coefficients are as high as 11.7 × 10−6 K−1 (1200 °C). The unique ferroelasticity and outstanding thermophysics properties indicate that SmNb1-XTaXO4 ceramics are promising thermal barrier coating materials.

Characterization of Ferroelastic Ceramics by Using Nano-Indentation

Characterization of Ferroelastic Ceramics by Using Nano-Indentation

強弾性セラミクスの奇妙な機械的挙動

強弾性セラミクスの奇妙な機械的挙動

Influence of ferroelastic domains concentration on electrical resistance of YBa2Cu3O7-δ ceramics

ABSTRACTDependence of the resistivity (ρ) of YBa2Cu3O7-δ ferroelastic ceramics on a cycle varying shear stress (σ) have been studied experimentally at room temperature. Obtained ρ(σ) loop has a shape of a “butterfly.” The analysis of ρ(σ) dependence shape revealed the relationship of the resistivity ρ with a concentration of elastic domain boundaries. Increasing of ρ with domain boundary concentration probably caused by charge carries scattering on domain boundaries and decreasing of their mobility.

Characterization of the geometry of microscale periodic structures using acoustic microscopy

Periodic structures are very common in both scientific investigations and engineering applications. The geometry of the periodic structure is important for its designed functionality. Although the techniques such as optical and electron microscopy are capable of measuring the periodicity of microscale periodically-corrugated structures, they cannot be used to measure the height or depth of the corrugation. The technique of acoustic microscopy has been developed rapidly and it has been applied in the studies of steel integrated structures, ferro-elastic ceramics, human retina, semiconductors, composites, etc. In acoustic microscopy, V(z) curves have been used to investigate the visco-elastic parameters of thin sliced samples of composites, animal tissue, etc., while in this work it is applied in characterizing the geometry of periodically corrugated structures. The measurements of the geometry of periodic structures obtained using acoustic microscopy are compared with those obtained using optical microscopy, and the reliability of this acoustic technique is also examined.

Comparison of neutron diffraction and Raman spectroscopic studies of the ferroelastic behavior of ceria-stabilized zirconia at elevated temperatures

Abstract Measurements of coercive stress for ferroelastic switching were made for 18-mol% ceria-stabilized zirconia under compressive loading using both neutron diffraction and Raman spectroscopy to validate the accuracy of those made by Raman against standard neutron diffraction measurements. Good agreement was observed between the two techniques and as a result, Raman scattering was identified as an effective technique for measuring coercive stresses in ferroelastic ceramics. In addition to absolute measurements in coercive stress, it was confirmed that coercive stress remains invariant in neutron diffraction measurements ranging from room temperature to 1200 °C. This suggests measurements of coercive stress measured using Raman spectroscopic techniques at room temperature are relevant to toughening mechanisms active at turbine operating conditions.

Advanced Nano-Scale Metrology for the Characterization of Ceramic Materials in the Scanning Electron Microscope

With the proliferation of several types and classes of high performance ceramic materials, the screening, evaluation and integration of new materials into structures and devices require a new and more effective approach. Evaluation on the nano-scale of the mechanical characteristics of new ceramic materials requires multiple complementary metrology tools. We report here about an advanced metrology tool, cathodoluminescence (CL) spectroscopy, which has a potential to rapidly screen and evaluate residual stress characteristics in advanced ceramic materials and structures. Nano-scale stress measurements are made in situ into an integrated metrology vacuum chamber in a field-emission gun scanning electron microscope (FEG-SEM). Complementing this tool, we also describe a new image analysis based on CL emission for fast screening and ranking of domain structures in ferroelastic ceramics. The end result of this paper is to show how crystallographic and mechanical characteristics of ceramics can be quantitatively characterized in a hybrid device combining electro-stimulated imaging and spectroscopic outputs.

Characterization of domain structures from diffraction profiles in tetragonal ferroelastic ceramics

The underlying domain structures of ferroelastic ceramics have a large influence on their macroscopic electromechanical properties. The profile shape functions of certain pseudo-cubic peaks in diffraction patterns collected from these materials can provide a great deal of information about such domain structures. Using both constant-wavelength neutron and high-energy synchrotron x-ray diffraction, profile shape functions of the pseudo-cubic 002 reflection are evaluated in a soft, tetragonal PZT ceramic. Errors in the integrated intensity ratio, important for measuring the degree of domain boundary movement in these materials, are subject to further scrutiny. It is shown that an asymmetric Pearson VII type distribution, integrated numerically between reasonable limits, gives the most accurate value of relative domain populations in these materials. It is also shown that the diffuse scattering caused by ferroelastic domain walls may be used to estimate the amount of material that is affected by microstrains originating at these walls.

R‐Curve and Stress–Strain Behavior of Ferroelastic Ceramics

The R‐curve and stress–strain behaviors in a variety of ferroelastic polycrystalline ceramic compositions are investigated and compared. These include soft and hard compositions of Pb(Zr,Ti)O3, Na0.5Bi4.5Ti4O15, PbNb2O6, PbTiO3, and Pb(Mg1/3Nb2/3)O3–Pb(Zr,Ti)O3. The fracture toughness enhancement is the highest in the soft PZT ceramic. The material parameters which influence the ferroelastic contribution to the toughness enhancement are extracted from the stress–strain behavior and compared with the measured toughness enhancement. Limited ferroelastic toughening is expected in the PbNb2O6 and Na0.5Bi4.5Ti4O15 compositions yet they exhibit a relatively large toughness enhancement. This toughness enhancement is attributed to frictional crack bridging through an exceptional intergranular fracture path. The frictional bridging effects are relieved by thermal annealing indicating some ferroelastic assistance in this mechanism.

Determination of domain orientation in lead zirconate titanate ceramics by Raman spectroscopy

Raman spectroscopy was employed to investigate the domain orientations of poled and unpoled tetragonal lead zirconate titanate ceramics. Using backscattering geometry, the ceramics were rotated 360° relative to the polarization direction of the incident beam. The ratio of the crossed to parallel polarization intensities in the poled sample demonstrates periodicity with respect to the rotation angle, while that of the unpoled sample does not. The angular periodicity of the intensity ratio is related to the domain orientations through the Raman tensor. Raman spectroscopy is thereby demonstrated as a quantitative technique that can measure domain switching distributions in ferroelastic ceramics.

Saturated domain switching textures and strains in ferroelastic ceramics

This paper introduces saturated domain switching textures of three different ferroelastic ceramic crystal systems. The accompanying extrinsic domain switching strain is calculated exclusively using a volume-weighted integral of a single pole figure. In ceramics which are also ferroelectric, the electromechanical response is defined by the domain switching textures, strains, and strain asymmetry, which are found to be functions of the number and directions of possible ferroelastic structural distortions.

Constitutive Law for Ferroelastic and Ferroelectric Piezoceramics

The focus of this paper is to investigate the nonlinear behavior exhibited by ferroelectric and ferroelastic ceramics under high electromechanical loading. External loads, such as electric field and stress, can induce a remanent strain or polarization due to domain switching. Two internal variables are introduced in order to capture the history dependance and dissipation that characterize ferroelectricity and ferroelasticity. Two loading surfaces are introduced so that associated flow rules provide the evolution laws of the internal variables. In addition, these variables must verify kinematical constraints that may depend on the stress state since experiments indicate that tensile and compressive states have to be considered in this order. Then, dielectric, butterfly, and ferroelastic hysteresis are represented. Mechanical depolarization is also captured. All the tangent operators are expressed so that a resolution with a finite element method can be achieved.