Figure 5 - uploaded by Zhao Pan
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Map of electron density change before and after the formation of chemical bonds (electron density difference, EDD) in the (010) plane. The Ti, Co, and O atoms are represented by gray, blue, and red balls, respectively, and M indicates the Mulliken population.
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Zero thermal expansion (ZTE) behavior is rare but important for both fundamental studies and practical applications of functional materials. Until now, most available ZTE materials are either electrical insulating oxides or conductive metallic compounds. Very few ZTE materials exhibit the semiconductor feature. Here we report a ZTE in a semiconduct...
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Context 1
... this model the parent PbTiO 3 lattices were not considered because they are not involved in the Ti−Co substitution. As shown in Figure 5, the Ti and Co atoms are located on the different (001) planes, coordinated to the neighbor "bridging" or "dangling" oxygen atoms. The electron density difference (EDD) maps in the (010) plane (as shown in Figure 5) clearly show that many more electrons are accumulated on the Ti−O bonds as compared with the Co−O bonds, revealing the stronger bond strength of the former. ...
Context 2
... shown in Figure 5, the Ti and Co atoms are located on the different (001) planes, coordinated to the neighbor "bridging" or "dangling" oxygen atoms. The electron density difference (EDD) maps in the (010) plane (as shown in Figure 5) clearly show that many more electrons are accumulated on the Ti−O bonds as compared with the Co−O bonds, revealing the stronger bond strength of the former. This conclusion is also demonstrated by the Mulliken population 35 analysis, i.e., the bond orders of Ti− O bonds are much larger than those of Co−O bonds. ...
Context 3
... conclusion is also demonstrated by the Mulliken population 35 analysis, i.e., the bond orders of Ti− O bonds are much larger than those of Co−O bonds. Therefore, the oxygen atoms connected to Co atoms are easier to remove to form the oxygen vacancies; the formation energies for oxygen vacancies at the sites around Co atoms are smaller than those around Ti atoms (also labeled in Figure 5). This explains the experimental observations that the content of oxygen vacancies increases as more Co atoms are incorporated into the crystal lattice ( Figure S12). ...
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Citations
... 23 Owing to the flexible perovskite structure of PT, its piezoelectric and thermal expansion properties can be easily modified by chemical substitutions. 2 In particular, zero thermal expansion can be successfully achieved in PT-based piezoelectric materials. 43,44 Bi 0.5 K 0.5 VO 3 is isostructural with PT and can also be regarded as a promising matrix to form the so-called morphotropic phase boundary with excellent piezoelectric properties. 45 ...
... 6 Ideally, ZTE materials should be single phase rather than composites due to the advantage of higher mechanical performance, lower internal stress, and easier preparation. 7,8 There are very few single-phase ZTE materials reported to date. Examples include Invar with formula Fe 0.65 Ni 0.35 or related Inovco alloys, 4 Mn 3 Cu 1−x Ge x N 3 , 9 Mn 3 (Cu 0.55 Sn 0.45 )-N, 10 Zr 0.4 Sn 0.6 Mo 2 O 8 , 11 (Sc 1−x M x )F 3 (M = Ga and Fe), 8 and some PbTiO 3 (PT)-based ferroelectrics. ...
... The SEM-EDX maps analysis, indicated that the ceria ions did not segregate through the grain boundaries, instead, these cations dissolved within the ST lattice and encouraged the grain growth [30]. Table 1) were identified to be within the reported data [13,25,31]. In the Sr 0.85 Ce 0.1 TiO 3 compound, the bonding between oxygen and Ti is not fully ionic, hence, the ground state of the compound cannot be indicated by O 2and Ti 4+ , but by a mixture of Ti 4+ and Ti 3+ [31]. ...
... Table 1) were identified to be within the reported data [13,25,31]. In the Sr 0.85 Ce 0.1 TiO 3 compound, the bonding between oxygen and Ti is not fully ionic, hence, the ground state of the compound cannot be indicated by O 2and Ti 4+ , but by a mixture of Ti 4+ and Ti 3+ [31]. The O-1s binding energy region is markedly wider and the peak nearly at 529.7 eV is attributed from both Ce-O and Ti-O, which have comparable B.E [13,25]. ...
The SrO-TiO2-CeO2 (Sr1−1.5×CexTiO3, SCTO, 0 ≤ x ≤ 0.2, sintered in N2) solid solution exhibited the existence of dielectric abnormality/anomaly (for polished samples) and high-permittivity microwave dielectric properties (for unpolished samples). X-ray diffraction (XRD) and Rietveld refinement, along with high-resolution transmission electron microscopy (HRTEM), indicated the evidence of cubic like structure. The SEM-EDX maps demonstrated the formation of a complete solid solution, which further support the XRD results. X-ray photoelectron spectroscopy (XPS) analysis showed mixture of ion valence states upon lattice defects formation. The activation of the TO2/TiO4 polar bands usually described a relaxor-type-dielectric anomaly. The ε′-T curve, together with the polar nature measurements exhibited hysteresis loops, indicating that ceria ions induced weak relaxor behavior. The observed Q×f values were primarily dependent on the lattice defects and Ti³⁺ cations. The temperature coefficient of resonant frequency (τf) shifted gradually from more positive (+1321 ppm/°C) to less positive (+539 ppm/°C) values with a rise of Ce content (x). The unpolished sample with x = 0.2 exhibited a high permittivity microwave dielectric properties with εr = 182, τf = +539 ppm/°C, and Q×f = 668 GHz.
... The enhanced tetragonality should be closely related to the large P S displacements induced by the strong Pb/Bi-O hybridization and coupling interactions between Ti/Zn and Pb/Bi cations. 25,26 Generally, large tetragonality in the PT-based piezoelectric materials is usually accompanied by intriguing physical scenarios such as large P S and high T C . ...
PbTiO3-Bi(Zn1/2Ti1/2)O3 is considered to be a promising high ferroelectric performance material in the Pb/Bi-based perovskite family. In the present study, a whole set of (1-x)PbTiO3-xBi(Zn1/2Ti1/2)O3 (0 ≤ x ≤1) solid solutions have been prepared by the conventional solid-state and high-pressure vs high-temperature methods. The effect of Bi(Zn1/2Ti1/2)O3 on the crystal structure has been investigated by synchrotron X-ray powder diffraction. Unlike most PbTiO3-based perovskites, the present system exhibits a continuously enhanced tetragonality (c/a) and large spontaneous polarization (PS) by the substitution of isostructural Bi(Zn1/2Ti1/2)O3. The enhanced c/a is ascribed to the large spontaneous polarization displacements induced by the strong Pb/Bi-O hybridization and coupling interactions between Ti/Zn and Pb/Bi cations, which can be evidenced by the lattice dynamics study and first-principles calculations. Accordingly, the TC is expected to be approximately 1000 ºC if its perovskite structure can be stabilized. The present study provides a route to obtain large-PS PbTiO3-based ferroelectric materials by introducing isostructural perovskites with strong polarity.
Materials with negative thermal expansion (NTE) attract significant research attention owing to their unique physical properties and promising applications. Although ferroelectric phase transitions leading to NTE are widely investigated, information on antiferroelectricity‐induced NTE remains limited. In this study, single‐crystal and polycrystalline Pb2CoMoO6 samples are prepared at high pressure and temperature conditions. The compound crystallizes into an antiferroelectric Pnma orthorhombic double perovskite structure at room temperature owing to the opposite displacements dominated by Pb²⁺ ions. With increasing temperature to 400 K, a structural phase transition to cubic Fm‐3m paraelectric phase occurs, accompanied by a sharp volume contraction of 0.41%. This is the first report of an antiferroelectric‐to‐paraelectric transition‐induced NTE in Pb2CoMoO6. Moreover, the compound also exhibits remarkable NTE with an average volumetric coefficient of thermal expansion αV = −1.33 × 10⁻⁵ K⁻¹ in a wide temperature range of 30–420 K. The as‐prepared Pb2CoMoO6 thus serves as a prototype material system for studying antiferroelectricity‐induced NTE.
Zero‐thermal‐expansion (ZTE) alloys, as dimensionally stable materials, are urgently required in many fields, particularly in highly advanced modern industries. In this study, high‐performance ZTE with a negligible coefficient of thermal expansion av as small as 2.4 ppm K−1 in a broad temperature range of 85–245 K is discovered in Hf0.85Ta0.15Fe2C0.01 magnet. It is demonstrated that the addition of trace interstitial atom C into Ta‐substituted Hf0.85Ta0.15Fe2 exhibits significant capability to tune the normal positive thermal expansion into high‐performance ZTE via enhanced magnetoelastic coupling in stabilized ferromagnetic structure. Moreover, direct observation of the magnetic transition between ferromagnetic and triangular antiferromagnetic states via Lorentz transmission electron microscopy, along with corresponding theoretical calculations, further uncovers the manipulation mechanism of ZTE and negative thermal expansion. A convenient and effective method to optimize thermal expansion and achieve ZTE with interstitial C addition may result in broadened applications based on the strong correlation between the magnetic properties and crystal structure. Zero thermal expansion (ZTE) with a negligible coefficient of thermal expansion av of 2.4 ppm K−1 in a broad temperature range is achieved owing to the significant contribution of interstitial C into a Hf–Ta–Fe magnet. The corresponding mechanism of tuning normal positive thermal expansion into intriguingly ZTE via enhanced magnetoelastic coupling during magnetic transition is clarified by comprehensive property measurements, direct observation of magnetic transition, and theoretical calculations.
In this work, Ni-doped lead-free ferroelectric Ba(Ti0.8Zr0.2)O3 materials were well synthesized by a simple chemical route. The complex magnetic behavior of the materials was explained by the random distribution of Ni cations into the Ba(Ti0.8Zr0.2)O3 host lattice. As increasing the Ni concentration to 9 mol%, nonlinear electric polarization behavior remained unchanged in the Ba(Ti0.8Zr0.2)O3 materials. The observations in nonlinear magnetization and electric polarization in Ni-doped Ba(Ti0.8Zr0.2)O3 materials suggested an extension of new material functions to the development of advanced materials for electronic devices.
Combination in both ferroic properties in current lead-free ferroelectric materials is promising in creating a new type of smart electronic devices. In this report, single perovskite Co-doped 0.2BaZrO3-0.8BaTiO3 materials were synthesized by using the chemical method. The random incorporation of Co cations into the host lattice of 0.2BaZrO3-0.8BaTiO3 compounds resulted in distortion of the lattice parameter and strong reduction the optical band gap energy. Decreasing optical band gap energy was obtained from around 3.17 to 2.52 eV by introducing Co concentration of up to 9 mol.%. The magnetic properties of 0.2BaZrO3-0.8BaTiO3 compounds were showed in complex as dependent on the level of Co dopants. The nonlinear electrical polarization in 0.2BaZrO3-0.8BaTiO3 compounds was obtained and remained after the introduction of Co impurities. The observation in nonlinear in magnetism and electrical polarization were promised to transfer their materials for device applications.
A large linear negative thermal expansion (NTE) and expanded NTE temperature range (ΔTNTE) were obtained in magnetoelastic CrTe1-xSe
x
(0 ≤ x ≤ 0.15) compounds. For CrTe compound, its thermal expansion coefficient of volume (αV) was calculated to be -28.8 ppm K-1 with the temperature ranging from 280 to 340 K. Substituting Te with Se atoms, the NTE behavior and magnetic properties can be well manipulated. With increasing Se in CrTe1-xSe
x
(0 ≤ x ≤ 0.15) compounds, the ΔTNTE increases from 60 K (280-340 K for x = 0), to 80 K (240-320 K for x = 0.05), to 95 K (200-295 K for x = 0.1), and finally to 100 K (170-270 K for x = 0.15). Furthermore, a linear NTE remains independent of temperature for samples with x ≤ 0.1. The relationship between tunable NTE and magnetic properties was analyzed in detail, indicating that the NTE in CrTe1-xSe
x
compounds originates from the magnetovolume effect (MVE).
The exploring of large Negative thermal expansion (NTE) over a wide temperature range is an important subject in materials science, since the overall coefficient of thermal expansion (CTE) of ordinary materials can be effectively tailored by the introduction of NTE materials. Here we successfully achieved a large NTE within broad temperature range in a new Pb/Bi-based ferroelectric of (1-x)PbTiO3-xBi(Zn1/2V1/2)O3 by means of improving the ferroelectricity of PbTiO3. The present system exhibits an unusual enhanced tetragonality, a large spontaneous polarization (PS), and high Curie temperature (TC). Specifically, the x = 0.1 compound exhibits an enhanced CTE of -2.10 × 10⁻⁵/°C from room temperature (RT) up to its TC of 600 °C, which is contrasted to that of pristine PbTiO3 (-1.99 × 10⁻⁵/°C, RT - 490 °C). More intriguingly, large volume shrinkages (ΔV ≈ -1%) have also been observed during the ferroelectric-to-paraelectric phase transition. According to the experimental and theoretical studies, the large NTE is attributed to the enhanced PS derived from the strong hybridization of Pb/Bi-O and Ti/Zn/V-O through the substitution of polar Bi(Zn1/2V1/2)O3 perovskite. The present study demonstrates that large NTE within wide temperature range can be achieved in PbTiO3-based ferroelectrics by improving its ferroelectricity through introducing isostructural polar perovskites.
