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By using pulsed laser deposition, Ba 0.95 La 0.05 PbO 3 (BLPO) thin films with different substrate temperatures (550–750 °C) and oxygen pressures (5–20 Pa) were prepared on SrTiO 3 (100) substrates. The charge valences of Ba and Pb cations in all the films are determined to be +2 and +4 by x-ray photoelectron spectroscopy. However, surface roughness of the films doesn’t keep unchanged, it increases with increasing temperature and oxygen pressure. The resistivity is significantly affected by substrate temperature and oxygen pressure, which increases with the former and decreases with the latter. Especially, the films deposited under 600 °C and 10 Pa oxygen pressure show metallic transport behavior with nearly temperature-insensitive values, as evidenced by the resistivity of 6.24×10 −5 Ω m and 5.41×10 −5 Ω m at 300 K and 15 K, respectively. Based on the structure and transport measurements, the optimized deposition conditions are determined to be close to 600 °C and 10 Pa. This work may provide some helpful clues for further work on tuning properties of BLPO films. [ABSTRACT FROM AUTHOR]

The study of ZrTe 5 is revived because theory predicts the quantum spin Hall effect in monolayer ZrTe 5 and topological phase in bulk ZrTe 5 . To study the topological property of ZrTe 5 , the growth of large size and high-quality single crystals is the first and crucial step. Here, by mean of iodine (I 2 ) transport agent, centimeter-sized ZrTe 5 single crystals were successfully grown by the chemical vapor transport technique. The microstructure characterization reveals that grown ZrTe 5 crystal has “stacking stripes of wood” morphology, and growth mechanism is proposed accordingly. The size of grown ZrTe 5 crystals can be reached as large as 35×2×0.5 mm 3 , which enable us to measure the a -, b - and c - axis anisotropic resistance. Large and single crystalline ZrTe 5 crystals provide a solid basis for exploring its topological phase. [ABSTRACT FROM AUTHOR]

Lead-free ceramic-based dielectric capacitors with high-performance energy storage properties have become an emerging issue recently as a result of the applications in high-power and/or pulsed-power technologies. However, the trade-off between various parameters, such as maximum polarization P max , remnant polarization P r and dielectric breakdown strength E b , restricts the further improvement of the energy storage properties of dielectric ceramics. Herein, a synergistic optimization strategy via simultaneous enhancement of P max and E b and reduction of P r is adopted to achieve outstanding energy storage properties for Bi 0.9 La 0.1 FeO 3 -Ba 0.7 Sr 0.3 TiO 3 NaNb 0.85 Ta 0.15 O 3 relaxor ferroelectric ceramics, characterized by an ultrahigh recoverable energy density W rec of 15.9 J/cm3 and high efficiency η of 87.7%. The inborn gene of BiFeO 3 -based materials results in high P max and the improved relaxor behavior gives rise to a small P r value. In Particular, a very large value for E b is obtained by tailoring multiple intrinsic and extrinsic factors. These results demonstrate the reliability and feasibility of the multiple optimization strategy proposed in this work to develop novel dielectric ceramics for advanced energy storage applications. [Display omitted] [ABSTRACT FROM AUTHOR]

K x RhO 2 , as an isomorphism material to Na x CoO 2 , is theoretically predicted to have rich physical properties. In this letter, we studied the chemical depotassiation process of K 0.62 RhO 2 crystals to obtain K x RhO 2 with x varied from 0.32 to 0.62. And an end-product K 0.32 RhO 2 with single phase determined through XRD refinement belongs to space group P6 3 /mmc (No. 194). Electrical transport, magneto-resistant transport and Hall measurements substantiate that K 0.32 RhO 2 is a multi-band normal metal, which can be well described by Landau Fermi liquid theory. Our finding sheds more light on the preparation and transport properties of layered oxides. [ABSTRACT FROM AUTHOR]

Ferroelectric/polar semiconductor BaTiO 3 : x ZnO composites (BT: x ZnO) have been prepared and investigated. The ZnO particles distribute at the BT grain boundaries to form 0–3 type composites, i.e., the isolated 0-dimensional ZnO particles are embedded in the 3-dimensional BT matrix. With increasing ZnO content, the Curie temperature keeps constant, however, both the dielectric constant and ferroelectric polarization of the composites increase, reaching the maximum at x =0.3, and then tend to decrease. Furthermore, the composite has improved temperature stability of ferroelectric polarization and field-induced strain up to ~100 °C. It is believed that ZnO can induce a built-in electric field which has influence on the domain switching and thus on the observed composition- and temperature-dependent electrical properties. This work may provide some new clues for developing ferroelectric composites with high performance. [ABSTRACT FROM AUTHOR]

Abstract: Electron-doped Ba1−x La x PbO3 (x≤0.30) ceramics have been prepared; the phase, microstructure, and conductivity have been investigated as functions of x value and sintering temperature. The solution limit is close to x=0.15. Sintering temperature plays an important role in determining phase purity and microstructure (grain size and porosity). All single-phase ceramics show metallic nature, which is related to two main factors. On the one hand, electron-doping increases the resistivity from 10−8 Ωm for the composition with x=0 to 10−5 Ωm for others with x≠0. On the other hand, the effect of grain size and porosity on resistivity is considerable, though not as significant as that of electron-doping. The structure–property relationship is discussed in detail. Our results may be helpful for further work on BaPbO3-based materials. [Copyright &y& Elsevier]

A series of Gd-doped Sr 2 IrO 4 single crystals were grown using a flux method. Analysis of the temperature-dependent resistance of these crystals reveals that these samples show two-dimensional weak localization at 150 to 300 K, while three-dimensional variable range hopping (VRH) behavior is observed at temperatures lower than 150 K. Two localization lengths are observed in the VRH behavior, with a transition temperature of around 88 K. Correspondingly, temperature-dependent magnetization observations along the ab -plane reveal magnetic anomalies at both 150 and 85 K. This work demonstrates the correlation between the electrical and magnetic properties of 5 d transition-metal compounds. [ABSTRACT FROM AUTHOR]

Abstract: Triple perovskite Sr3MFeMoO9 (M=Mn, Co, Ni) ceramics have been prepared under flowing N2 steam. All compositions are single phase and have B-site cation ordering. However, the composition with M=Co shows denser microstructures with smaller grains, the average grain sizes are 700, 500 and 650nm for M=Mn, Co, and Ni, respectively. The chemical states of the surface and interior Mn, Co, Ni, Fe, and Mo cations are analyzed carefully. Both the magnetization-magnetic field curves and magnetization–temperature curves confirm that all compositions show antiferromagnetic behaviors. The Néel temperature of M=Mn and Ni compositions are determined to be 24.4 and 49.5K, respectively. However, M=Co composition shows two magnetic transition temperatures at 70.9 and 180.7K, which is possibly attributed to that the Co cations have intermediate spin-state (3d 6, S=1) and high spin states (3d 6, S=2). Furthermore, the compositions show semiconductor-like behaviors and neglectable magnetoresistance in whole measuring temperature range. Our results may be helpful for designing novel magnetic materials and for understanding magnetic couplings in triple perovskites. [Copyright &y& Elsevier]

Sr2 FeMoO6 ceramics with different Fe/ Mo antisite defect ( ASD) concentrations and grain-boundary ( GB) properties were prepared. The competitive and combining effects of GB and Fe/ Mo ASD on the transport and magnetoresistance were discussed. The GB properties, that is, intergrain coupling strength, positively related with resistivity value, is extremely sensitive to the total flux of reducing gas, in general, lower total gas flux leads to larger resistivity, thus stronger intergrain coupling strength, and then the contributions of GB effect to low-field magnetoresistance ( LFMR) increase appreciably regardless of the amount of ASD. In detail, when ASD concentration is less than 26%, LFMR is dominantly controlled by the GB effect. However, the suppressed ASD effect on LFMR behavior comes to play when the ASD content is larger than or equal to 26%, where the GB and ASD effects contribute together to the LFMR. [ABSTRACT FROM AUTHOR]

Abstract: High quality double perovskite Sr2Fe10/9Mo8/9O6 thin films have been prepared on (111)-SrTiO3 substrates under different N2 partial pressures (0.1–20Pa). The films are (111)-oriented with flat surfaces and sharp film/substrate interfaces. The epitaxy and local Fe/Mo ordering are revealed by high resolution transmission electron microscopy and selected area electron diffraction. It is established that the N2 pressure has significant effects on structures and properties: With increasing N2 pressure, the film thickness decreases and the strain increases, while the magnetization decreases monotonously. Interestingly, all the films show semiconductor-like behavior in the whole measuring temperature range but the resistivity increases with increasing N2 pressure. The observed results are attributed to that N2 pressure can affect the strain and the concentration of Fe–O–Mo, both play important roles in magnetic interaction, and thus affect the magnetic and transport behaviors. [Copyright &y& Elsevier]

Abstract: Double perovskite Sr2CrWO6 films have been prepared on SrTiO3 (111) substrates by pulsed laser deposition in high vacuum (10−5 Pa). X-ray diffraction patterns indicate that the films are (111)-oriented. Both atomic force microscopy (AFM) and cross-section transmission electron microscopy (TEM) images prove that the films have very smooth surfaces. Detailed microstructures given by high resolution transmission electron microscopy (HRTEM) further confirm that the films are epitaxial with sharp and coherent substrate/film interface. Well saturated magnetization–magnetic field hysteresis loop is observed with the saturation magnetization of 1.2μB/formula unit at 10K. The films show metallic transport behavior and large positive magnetoresistance (∼180% at 10K). The structure–property relationship is discussed in detail. [Copyright &y& Elsevier]

A novel ferromagnetic triple perovskite Sr3CrFeMoO9 was designed and ultrathin films were fabricated. The films are highly strained, with a sharp film/substrate interface. The valences of the Cr, Fe and Mo cations are +3, +3 and +6, respectively. Well-saturated ferromagnetic hysteresis loops are observed at room temperature and 10K, and the Curie temperature should be higher than 400K, as indicated by the temperature–magnetization curve. The films show semiconductor-like behavior with almost negligible magnetoresistance. The possible spin configuration is analyzed based on experimental results. [ABSTRACT FROM AUTHOR]

Highlights: [•] Systematically and comparative microstructure analysis for the SrIrO3 thin films. [•] Meta-stable orthorhombic SrIrO3 phase was obtained under normal conditions. [•] The stabilization of meta-stable orthorhombic SrIrO3 was quantitatively understood by lattice mismatch strain. [ABSTRACT FROM AUTHOR]

Abstract: Lead-free piezoceramics of (1− x)Ba0.8Sr0.2TiO3–xBiAlO3 [(1− x)BST–xBA (0≤ x ≤0.12)] have been synthesized and the structures and properties have been investigated systemically. X-ray diffraction patterns indicated that the solid solution limit is close to x =0.04, and a morphotropic phase boundary (MPB) separating tetragonal and pseudocubic phases exists near x =0.02. The ferroelectricity weakens monotonously with increasing x, accompanied by weakened butterfly shaped bipolar strain–electric field curves. The temperature dependent properties of the composition with x =0.02 have been typically investigated, showing that with increasing temperature, the ferroelectricity tends to be weakened. Pure electrostrictive effect has been found in the compositions with x =0.02 and 0.03 close to room temperature temperature. Based on the results, the effects of BA on structures and electric properties were discussed. [Copyright &y& Elsevier]

Abstract: Orthorhombic YMnO3 thin films were epitaxially grown on bare and LaNiO3 buffered (001)–SrTiO3 substrates by pulsed laser deposition under various oxygen pressures from 5 to 30Pa. The crystal structure and microstructure of these films have been characterized by both X-ray diffractions and transmission electron microscopy. The leakage current, modeled as the space charge limited current (SCLC) mechanism, decreased significantly with the increase of oxygen content. It is further found that the magnetic property of films is greatly enhanced in YMnO3 films grown under high oxygen pressure, which can be explained decreased oxygen vacancies. In addition, bipolar switching behavior was obtained only in the films grown under 30Pa oxygen pressure, which is attributed to the decrease of voltage-driven oxygen vacancy migration. [Copyright &y& Elsevier]

Abstract: A series of lead-free piezoceramics of (1− x)K0.5Na0.5NbO3–xBi0.8La0.2FeO3 [(1− x)KNN–xBLF, 0.005≤ x ≤0.04] were synthesized by conventional solid-state sintering. Crystal structures and microstructures of the ceramics were characterized by X-ray diffraction and transmission electron microscopy. X-ray diffraction substantiates the existence of an orthorhombic-tetragonal morphotropic phase boundary (MPB) near x =0.01. Highest electrical performances were observed near the MPB. The maximum remnant polarization, piezoelectric coefficient, and coupling factor were measured as 22.5μC/cm2, 144pC/N, and 0.34, respectively. The effects of BLF on structures and electrical properties were discussed. Our results might be helpful for developing KNN-based piezoelectric ceramics. [ABSTRACT FROM AUTHOR]

Abstract: Magnetoresistance (MR) of transition metal (TM)-doped and co-doped ZnO films prepared by a magnetron sputtering system has been discussed. For single-doped film, the values of H max (the field at which MR shows its maximum) increase as temperature increases. At a certain temperature, the values of H max increase from Mn-, Fe- to Co-doped films due to their different magnetic moments. For (Mn, Fe), (Mn, Co)-co-doped ZnO films, the MR behaviors show striking similarity as Mn-doped ZnO film. These results are interpreted in terms of the s–d spin-splitting mechanism. Large negative MR in high field is attributed to the formation of magnetic polarons (MPs). The temperature dependence of resistivity agrees well with the variable range hopping (VRH) mechanism of MPs. [Copyright &y& Elsevier]

Abstract: La-substituted BiFeO3, Bi0.8La0.2FeO3, thin films were fabricated on Pt/Ti/SiO2/Si substrates by pulsed laser deposition. X-ray diffraction and high-resolution transmission electron microscope were used to analyze the structures of the films. The results show the films fabricated under optimized growth condition are (012) textured. X-ray photoemission spectroscopy results indicate that the oxidation state of Fe ion is Fe3+ in the films without detectable Fe2+. The films show low leakage current and excellent dielectric characters. Multiferroic properties with a remnant ferroelectric polarization of 5.2μC/cm2 and a remanent magnetization of 0.02μB/Fe were established. These results have some implications for further research. [Copyright &y& Elsevier]

Abstract: Dual-radio frequency magnetron sputtering was employed to prepare (Mn, Co) co-doped ZnO films on sapphire (0001). X-ray diffraction and X-ray photoelectron spectroscopy results indicate that the films are highly c-axis oriented and the doped Mn and Co ions in films are both in the divalent states. A dominant photoluminescence peak was observed at the wavelength of 405 nm. Ultraviolet–Visible absorption spectra show band gaps of 2.80, 2.90, 3.27, and 3.22 eV for (Mn0.02, Co0.04) Zn0.94O, Zn0.90Co0.10O, Zn0.97Mn0.03O and ZnO films, respectively. A red-shift more than 500 meV was observed in a (Mn, Co) co-doped ZnO film. The Raman spectra measurement of (Mn, Co)ZnO films revealed additional vibrational modes at 276.6, 525.6, 634.6, and 643.9 cm−1 compared to the host phonons of ZnO. [Copyright &y& Elsevier]

[Display omitted] • Realizing stabilized antiferroelectric phase and enhanced relaxor behavior in (Na 1-3/2 x Bi 3/2 x)(Nb 1- x Mg x)O 3 ceramics. • The large E b of 78.3 kV/mm, ultrahigh W rec of 10.9 J/cm3 and high η of 83% were achieved in × = 0.06. • x = 0.06 exhibited superior frequency, fatigue, thermal stability and ultrafast discharge rate. Lead-free ceramic-based dielectric capacitors have attracted extensive investigation due to their potential applications in pulsed power devices. However, the main drawback of dielectric ceramics is the relatively low energy storage density. Herein, Bi3+ and Mg2+ with different ionic radius and valence are introduced into antiferroelectric NaNbO 3 matrix to form (Na 1-3/2 x Bi 3/2 x)(Nb 1- x Mg x)O 3 solid solutions, where the antiferroelectric phase is stabilized and the relaxor behavior is also improved. Of particular importance is that a large breakdown strength (E b) of 78.3 kV/mm, an ultrahigh recoverable energy density (W rec) of 10.9 J/cm3 and efficiency (η) of 83% are simultaneously achieved in (Na 0.91 Bi 0.09)(Nb 0.94 Mg 0.06)O 3 ceramic. Moreover, the energy storage properties of (Na 0.91 Bi 0.09)(Nb 0.94 Mg 0.06)O 3 ceramic also reveals superior frequency (1–100 Hz), cycling (100–105) and thermal (30°C–100°C) stability, together with the ultrafast discharge rate (<25 ns). These results demonstrate the NaNbO 3 -based lead-free relaxor antiferroelectric ceramics is a promising candidate for energy storage application. [ABSTRACT FROM AUTHOR]

● PLZST: x SnO 2 composite ceramics were prepared by solid state reaction. ● The composite structure had significant effects on microstructures and electrical properties. ● The optimal composition of x = 0.2 showed high energy storage density of 2.38 J/cm3. Constructing composite structure is an effective way to improve dielectric energy storage properties. However, ionic diffusion between composite members is generally inevitable, which mixes the effects of solid solution with composite structure on property to some extent. To exclude the ionic diffusion effect as much as possible, antiferroelectric (Pb 0.97 La 0.02)(Zr 0.5 Sn 0.4 Ti 0.1)O 3 (PLZST) was sintered at a relatively high temperature to precipitate SnO 2 particles, then more SnO 2 were introduced to from (1- x)PLZST: x SnO 2 (x = 0–0.25) composite. The results showed that composite structure had significant effects on microstructures and properties with changed lattice parameter, decreased grain size, increased Curie temperature, suppressed antiferroelectric property, and enhanced electric breakdown strength. The optimal composition of x = 0.2 showed high energy storage density of 2.38 J/cm3. This work provides a robust platform to investigate the effect of composite microstructure on electrical properties, which is helpful for further developing high performance composite materials. [ABSTRACT FROM AUTHOR]

Abstract: 1–3 and 2–2 types Pb(Zr0.53Ti0.47)O3–CoFe2O4 (PZT–CFO) composite films with controllable microstructures, consisted by CFO nanopillar embedded in PZT matrix and PZT–CFO gratings respectively, have been fabricated on Pt/Ti/SiO2/Si substrates by combining lithography technology and pulsed laser deposition. X-ray diffraction confirms that the films are well crystallized under optimized postannealing conditions. Scanning electron microscope reveals that the periodic microstructures can be well controlled. Especially, intrinsic room temperature ferroelectric and ferrimagnetic behaviors are observed simultaneously. The structure–properties relationship is discussed. Our results may provide an alternative method to design and prepare multiferroic composite films with controllable microstructures. [ABSTRACT FROM AUTHOR]

0.8Na 0.5 Bi 0.5 TiO 3 -(0.2- x)K 0.5 Bi 0.5 TiO 3 - x Bi(Zn 0.5 Ti 0.5)O 3 (NBT-KBT-BZT, x = 0–0.05 with interval of 0.01) lead-free piezoceramics were prepared and investigated. The addition of BZT has not led to deviation of rhombohedral-tetragonal morphotropic phase boundary, but apparently composition-dependent electrical property and monotonously improved thermal stability. The x = 0.02 has the optimal electrical property with remnant polarization, bipolar total strain, piezoelectric constant of 26.5 μC/cm2, 0.30%, 121 pC/N respectively, while the depolarization temperature is increased from 93 °C for x = 0–135 °C for x = 0.05 based on dielectric measurement. Detailed investigation reveals that the domain structure transforms from labyrinthian domain for x = 0 to coexistence of nanodomain and labyrinthian domain for x = 0.02, end up with large amount of nanodomain (x = 0.04). Such domain evolution should be responsible for the composition dependent electrical property and improved thermal stability. Our work confirms that domain engineering is an alternative method to develop high performance piezoelectric materials. • NBT-KBT-BZT lead-free piezoceramics have been prepared. • The piezoceramics show composition-dependent property and improved thermal stability. • Domain transforms from labyrinthian domain, coexisted nanodomain and labyrinthian domain, to nanodomain. [ABSTRACT FROM AUTHOR]

Piezoelectric ceramics with high electrical performances and high Curie temperature ( T c ) act as key materials for numerous electromechanical devices such as transducers and actuators. Herein, we report a systematic investigation on the crystal structure, microstructure and electrical properties of Sr and La co-doped Pb(Mg 1/3 Nb 2/3 )O 3 -PbZrO 3 -PbTiO 3 ceramics with a low Pb(Mg 1/3 Nb 2/3 )O 3 content, namely, (Pb 1- y Sr y )(Mg 1/3 Nb 2/3 ) 0.07 Zr x Ti 0.93- x O 3 : z La. With an increase in the Zr content ( x value) from 0.49 to 0.53, its crystal structure evolved from a tetragonal phase to a rhombohedral phase, leading to not only a morphotropic phase boundary (MPB) at around x = 0.51 but also a monotonously decreasing T c . Meanwhile, a change in either the Sr- or La-doping content ( y and z values, respectively) in the range of y = 0.03-0.07 and z = 0.01-0.03 can slightly deviate the structure of MPB, resulting in a significant effect on its electrical properties. As the best results, the optimal composition of x = 0.51, y = 0.05, and z = 0.02 yielded peak electrical performance, with a related room temperature piezoelectric coefficient ( d 33 ) of 645 pC N -1 , remanent polarization ( P r ) of 33.5 μC cm -2 , coercive field ( E c ) of 8.6 kV cm -1 , and T c of 242 °C. Especially, its piezoelectric properties showed excellent temperature stability, and its d 33 value decreased by only 3% from room temperature to 150 °C. This work not only provides an alternative piezoelectric ceramic with outstanding electrical performance for industrial applications, but also reveals a comprehensive perspective on the composition-structure-property relationship of doped Pb[(Mg 1/3 Nb 2/3 ),Zr,Ti]O 3 , which is helpful for further work on piezoelectric ceramics.

In conventional knowledge, ferroelectric solid solutions were formed between members belonging to the same crystal structure family. Since both tungsten bronze and perovskite structures are constructed by connecting the corner-sharing oxygen octahedra, it offers a possibility for formatting an unusual solid solution between these two families. Herein, (1 - x )Sr 0.6 Ba 0.4 Nb 2 O 6 - x BaTiO 3 , (1 - x )SBN- x BT, solid solutions were synthesized and the solution mechanism was resolved from a structure viewpoint. With increasing BT content, the solid solution persists of tetragonal tungsten bronze structure, but the lattice parameter a (= b ) decreases whereas c increases, resulting in the significant reduction of grains anisotropy. The ferroelectric-relaxor phase transition temperature shows a monotonic increase as x increases. However, the ferroelectricity evolution is not monotonous as a function of BT content because of the competitive effects of Ba and Ti on the property. As a result, the x = 0.10 ceramic shows the strongest ferroelectricity and a remarkable electrocaloric effect of 1.4 K near room temperature. This work challenges the traditional view of solid solution formation and provides an alternative way to modulate the structure and properties of ferroelectrics.

As the two typical basic binary solid solutions of the relaxor-PbTiO 3 family, Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 (PMN-PT) has been widely investigated, whereas Pb(Ni 1/3 Nb 2/3 )O 3 -PbTiO 3 (PNN-PT) has not. Here, 1.5 mol% Sm-doped (1 - x )Pb(Ni 1/3 Nb 2/3 )O 3 - x PbTiO 3 , (1 - x )PNN- x PT:0.015Sm with x = 0.33-0.39, ceramics have been prepared and the chemical composition-induced evolution of crystal structure, domain, and electrical properties investigated systematically. With increasing PT content, evolution of the rhombohedral-tetragonal structure was observed. A rhombohedral-tetragonal morphotropic phase boundary occurred around x = 0.36-0.37, which showed a peak piezoelectric property with piezoelectric constant d 33 = 531 pC N -1 and planar electromechanical coupling factor k p = 0.37 at room temperature. At the same time, the x = 0.36 composition showed improved ferroelectric behavior with remanent polarization P r = 13.4 μC cm -2 and coercive field E c = 3.2 kV cm -1 . Interestingly, different from its PMN-PT counterpart, there is no temperature-driven phase transition between room temperature and the Curie temperature for (1 - x )PNN- x PT:0.015Sm. These parameters indicated that the PNN-PT system is worthy of more attention and is a promising platform for further development of high-performance piezo/ferroelectric materials.

Rare-earth titanate pyrochlores have attracted considerable attention for their unique magnetic frustration. Among those compounds, Yb 2 Ti 2 O 7 , a candidate for quantum spin ice, has been extensively studied in its magnetic ground state. However, works on its dielectric property and structure-property relationship lag far more behind. Here, by preparing and investigating nonstoichiometric Yb 2- x Ti 2 O 7-δ ( x = 0-0.15) ceramics, we demonstrate that the samples with x ≤ 0.05 maintain a single-pyrochlore phase, but the nonstoichiometry arouses significant structural distortion and increased oxygen vacancy. As a result, the ferromagnetism, indicated by a positive Curie-Weiss temperature, decreases almost linearly with increasing x value. Remarkably composition-dependent low-temperature dielectric relaxations have been observed. In addition, through introducing nonstoichiometry, the relaxor degree of dielectric behavior is enhanced, and the dielectric curve shows an altered shape. The origin of this dielectric relaxation is attributed to the increased structural distortion reflected by the changed bond length/angle, since there is no phase transition in 90-300 K. Our work gives a comprehensive view on the structural, magnetic, and dielectric properties of Yb 2 Ti 2 O 7 , which is instructive for further work on pyrochlores.

Dielectric capacitors have attracted growing attention because of their important applications in advanced high power and/or pulsed power electronic devices. Nevertheless, the synergistic enhancement of recoverable energy storage density ( W rec > 10 J/cm 3 ) and efficiency (η > 80%) is still a great challenge for lead-free dielectric bulk ceramics. Herein, by introducing complex perovskite compound (Bi 0.9 Na 0.1 )(Fe 0.8 Ti 0.2 )O 3 with a smaller tolerance factor into an NaNbO 3 matrix (NN-BNFT), we have achieved and explored stable relaxor antiferroelectric ceramics with enhanced relaxor behavior. Of particular importance is the composition of 0.88NN-0.12BNFT, which exhibits a large electric breakdown strength E b of 87.3 kV/mm, an ultrahigh W rec of 12.7 J/cm 3 , and a high efficiency η of 82.5%, as well as excellent thermal reliability and an ultrafast discharge speed, resulting from the dense microstructure, the moderate dielectric constant, the reduced grain size, the dielectric loss, and the sample thickness. The outstanding energy storage properties of NN-BNFT display great promise in advanced dielectric capacitors for energy storage applications.

High-pressure experiments usually expect a hydrostatic condition, in which the physical properties of materials can be easily understood by theoretical simulations. Unfortunately, non-hydrostatic effect is inevitable in experiments due to the solidification of the pressure transmitting media under high pressure. Resultantly, non-hydrostaticity affects the accuracy of the experimental data and sometimes even leads to false phenomena. Since the non-hydrostatic effect is extrinsic, it is quite hard to analyze quantitatively. Here, we have conducted high pressure experiments on the layered BiCuXO (X = S and Se) single crystals and quantitatively analyzed their pronounced non-hydrostatic effect by high throughput first-principles calculations and experimental Raman spectra. Our experiments find that the BiCuXO single crystals sustain the tetragonal structure up to 55 GPa (maximum pressure in our experiment). However, their pressure-dependent Raman shift and electric resistance show anomalous behaviors. Through optimization of thousands of crystal structures in the high throughput first-principles calculations, we have obtained the evolution of the lattice constants under external pressures, which clearly substantiates the non-hydrostatical pressure exerted in BiCuXO crystals. Our work indicates that the high throughput first-principles calculations could be a handy method to investigate the non-hydrostatic effect on the structural and electronic properties of materials in high pressure experiments.

Sr 2 CrWO 6 /Sr 2 Fe 10/9 Mo 8/9 O 6 (SCWO/SFMO) superlattices with 4, 6, 7, 10 periods (abbreviated as S-1, S-2, S-3, and S-4) were prepared on (0 0 1) SrTiO 3 (STO) substrates by pulsed laser deposition. All superlattices show macroscopic ferromagnetic behavior, and the magnetization increases with increasing period. The S-1 superlattice demonstrates semiconductor-like temperature-dependent resistivity in the whole measuring temperature range and negative magnetoresistance of  -5.3% at 2 K with 2 T magnetic field, while the other superlattices illustrate metallic behaviors and increasing positive magnetoresistance of 223.1%, 275.4%, and 766.1% under the same conditions. This work not only provides a feasible way to tune the MR effect in magnetic perovskite oxides, but also may stimulate further work on artificially micro-structured thin films with designable magnetic properties.

As one of the most promising photocatalysts, graphitic carbon nitride (g-C 3 N 4 ) shows a visible light response and great chemical stability. However, its relatively low photocatalytic efficiency is a major obstacle to actual applications. Here an effective and feasible method to dramatically increase the visible light photocatalytic efficiency by forming C 3 N 4 /BiFeO 3 ferroelectric heterojunctions is reported, wherein the band alignment and piezo-/ferroelectricity have synergistic positive effects in accelerating the separation of the photogenerated carriers. At the optimum composition of 10 wt% BiFeO 3 , the heterojunction shows 1.4 times improved photocatalytic efficiency than that of the pure C 3 N 4 . Most importantly, mechanical pressing and electrical poling can also improve the photocatalytic efficiencies by 1.3 times and 1.8 times, respectively. The optimized photocatalytic efficiency is even comparable with that of some noble metal based compounds. These results not only prove the improved photocatalytic activity of the C 3 N 4 -ferroelectric heterojunctions, but also provide a new approach for designing high-performance photocatalysts by taking advantage of ferroelectricity.

Magnetoresistance (MR) is the magnetic field-induced change of electrical resistance. The MR effect not only has wide applications in hard drivers and sensors but also is a long-standing scientific issue for complex interactions. Ferromagnetic/ferrimagnetic oxides generally show negative MR due to the magnetic field-induced spin order. We report the unusually giant positive MR up to 17,200% (at 2 K and 7 T) in 12-nm Sr 2 CrWO 6 thin films, which show metallic behavior with high carrier density of up to 2.26 × 10 28 m -3 and high mobility of 5.66 × 10 4 cm 2 V -1 s -1 . The possible mechanism is that the external magnetic field suppresses the long-range antiferromagnetic order to form short-range antiferromagnetic fluctuations, which enhance electronic scattering and lead to the giant positive MR. The high mobility may also have contributions to the positive MR. These results not only experimentally confirm that the giant positive MR can be realized in oxides but also open up new opportunities for developing and understanding the giant positive MR in oxides.

Thin films of 0.85BiFe 1-2x Ti x Mg x O 3 -0.15CaTiO 3 (x = 0.1 and 0.2, abbreviated to C-1 and C-2, respectively) have been fabricated on (001) SrTiO 3 substrate with and without a conductive La 0.7 Sr 0.3 MnO 3 buffer layer. The X-ray θ-2θ and ϕ scans, atomic force microscopy, and cross-sectional transmission electron microscopy confirm the (001) epitaxial nature of the thin films with very high growth quality. Both the C-1 and C-2 thin films show well-shaped magnetization-magnetic field hysteresis at room temperature, with enhanced switchable magnetization values of 145.3 and 42.5 emu/cm 3 , respectively. The polarization-electric loops and piezoresponse force microscopy measurements confirm the room-temperature ferroelectric nature of both films. However, the C-1 films illustrate a relatively weak ferroelectric behavior and the poled states are easy to relax, whereas the C-2 films show a relatively better ferroelectric behavior with stable poled states. More interestingly, the room-temperature thermal conductivity of C-1 and C-2 films are measured to be 1.10 and 0.77 W/(m·K), respectively. These self-consistent multiferroic properties and thermal conductivities are discussed by considering the composition-dependent content and migration of Fe-induced electrons and/or charged point defects. This study not only provides multifunctional materials with excellent room-temperature magnetic, ferroelectric, and thermal conductivity properties but may also stimulate further work to develop BiFeO 3 -based materials with unusual multifunctional properties.

The microstructure of multiferroic LaFeO₃-YMnO₃ (LFO-YMO) multilayers grown on (001)- and (111)-SrTiO₃ substrates is characterized by the transmission electron microscopy (TEM). Detailed TEM characterization reveals that LFO-YMO multilayers grown on both substrates have clear layer-by-layer morphology and distinct chemical-composition layered structure. The most notable feature is that LFO-YMO multilayers grown on (001)-SrTiO₃ substrate have three types of domains, while those on (111)-SrTiO₃ have only one. The multi-/twin- domain structure can be qualitatively explained by the lattice mismatch in this system. The details of the domain structure of LFO-YMO multilayers are crucial to understanding their magnetic properties., Competing Interests: The authors declare no conflict of interest.

The asymmetric electron dispersion in type-II Weyl semimetal theoretically hosts anisotropic transport properties. Here, we observe the significant anisotropic Adler-Bell-Jackiw (ABJ) anomaly in the Fermi-level delicately adjusted WTe&#95;{1.98} crystals. Quantitatively, C&#95;{W}, a coefficient representing the intensity of the ABJ anomaly along the a and b axis of WTe&#95;{1.98} are 0.030 and 0.051  T^{-2} at 2 K, respectively. We found that the temperature-sensitive ABJ anomaly is attributed to a topological phase transition from a type-II Weyl semimetal to a trivial semimetal, which is verified by a first-principles calculation using experimentally determined lattice parameters at different temperatures. Theoretical electrical transport study reveals that the observation of an anisotropic ABJ along both the a and b axes in WTe&#95;{1.98} is attributed to electrical transport in the quasiclassical regime. Our work may suggest that electron-doped WTe&#95;{2} is an ideal playground to explore the novel properties in type-II Weyl semimetals.

The thickness-dependent metal-insulator transition is observed in meta-stable orthorhombic SrIrO3 thin films synthesized by pulsed laser deposition. SrIrO3 films with thicknesses less than 3 nm demonstrate insulating behaviour, whereas those thicker than 4 nm exhibit metallic conductivity at high temperature, and insulating-like behaviour at low temperature. Weak/Anderson localization is mainly responsible for the observed thickness-dependent metal-insulator transition in SrIrO3 films. Temperature-dependent resistance fitting shows that electrical-conductivity carriers are mainly scattered by the electron-boson interaction rather than the electron-electron interaction. Analysis of the magneto-conductance proves that the spin-orbit interaction plays a crucial role in the magneto-conductance property of SrIrO3.