Search

A series of lead-free (K0·49Na0·49Li0.02) (Nb0·8Ta0.2)O3 (KNLNT) piezoelectric ceramics modified by CaZrO3 (denoted as KNLNT-xCaZrO3, x = 0–0.05) were synthesized using a conventional solid-state approach. Herein, the influence of CaZrO3 doping on the crystal structure, ferroelectric properties, dielectric properties as well as piezoelectric properties were systematically investigated. The XRD analysis shows that all the proposed samples present pure perovskite phase, revealing the phase structure transition from an orthorhombic to a pseudocubic phase at a threshold value of x is 0.01 and 0.03. Moreover, the in-situ XRD characterization was applied to investigate the transformation process of phase structure: the pseudocubic-tetragonal (TP-T) phase transition temperature has been decreased to room temperature at x = 0.04. In addition, the results were further confirmed by the temperature-dependent dielectric properties. For the microstructure, the typical strip-like domains and nanoscale domains can be found in transmission electron microscopy (TEM) images. Due to the coexistence of orthorhombic and pseudocubic with x = 0.03, the remnant polarization has an anomaly, and large strain value and large signal d33* value is obtained under a 20 kV/cm electric field, which is about 0.106% and 532 pm/V.

Taking advantage of the unique layered structure of TiSe2, the intrinsic electronic properties of two-dimensional materials can easily be tuned via heteroatomic engineering. Herein, we show that the charge density wave (CDW) phase in 1T-TiSe2 single-crystals can be gradually suppressed through Sn atoms intercalation. Using angle-resolved photoemission spectroscopy (ARPES) and temperature-dependent resistivity measurements, this work reveals that Sn atoms can induce charge doping and modulate the intrinsic electronic properties in the host 1T-TiSe2. Notably, our temperature-dependent ARPES results highlight the role exciton-phonon interaction and the Jahn-Teller mechanism through the formation of backfolded bands and exhibition of a downward Se shift of 4p valence band in the formation of CDW in this material.

Recently discovered kagome metals AV3Sb5 (A = K, Rb, and Cs) provide an ideal platform to study the correlation among nontrivial band topology, unconventional charge density wave (CDW), and superconductivity. The evolution of electronic structures associated with the change of lattice modulations is crucial for understanding of the CDW mechanism, with the combination of angle-resolved photoemission spectroscopy (ARPES) measurements and density functional theory calculations, we investigate how band dispersions change with the increase of lattice distortions. In particular, we focus on the electronic states around M ¯ point, where the van Hove singularities are expected to play crucial roles in the CDW transition. Previous ARPES studies reported a spectral weight splitting of the van Hove singularity around M ¯ point, which is associated with the 3D lattice modulations. Our studies reveal that this “splitting” can be connected to the two van Hove singularities at kz = 0 and kz = π/c in the normal states. When the electronic system enters into the CDW state, both van Hove singularities move down. Such novel properties are important for understanding of the CDW transition.

The intercalation of transition metal atoms into the van der Waals gap of the layered transition metal dichalcogenides (TMDCs) results in modulations of electronic structures and transport properti...

The intercalation of metal is a promising method for the modulating electronic properties in transition metal dichalcogenides (TMDs). However, there still lacks enough knowledge about how the intercalated atoms directly impact the two-dimensional structural layers and modulate the band structures therein. Taking advantage of X-ray absorption fine structure and angle-resolved photoemission spectroscopy, we studied how Cu intercalation influences the host TaSe2 layers in Cu0.03TaSe2 crystals. The intercalated Cu atoms form bonds with Se of the host layers, and there is charge transfer from Cu to Se. By examining the changes of band dispersions, we show that the variation of electronic structures is beyond a simple rigid band model with merely charge doping effect. This work reveals that the unusual change of band dispersions is associated with the formation of bonds between the intercalated metal elements and anion ions in the host layers, and provides a reference for the comprehensive understanding of the electronic structures in intercalated materials.

The non-symmorphic crystal symmetry protection in the layered topological semimetal Nb

Tuning the bandgap in layered transition metal dichalcogenides (TMDCs) is crucial for their versatile applications in many fields. The ternary formation is a viable method to tune the bandgap as well as other intrinsic properties of TMDCs, because the multi-elemental characteristics provide additional tunability at the atomic level and advantageously alter the physical properties of TMDCs. Herein, ternary Ti x Zr1 – x Se2 single crystals were synthesized using the chemical-vapor-transport method. The changes in electronic structures of ZrSe2 induced by Ti substitution were revealed using angle-resolved photoemission spectroscopy. Our data show that at a low level of Ti substitution, the bandgap of Ti x Zr1 – x Se2 decreases monotonically, and the electronic system undergoes a transition from a semiconducting to a metallic state without a significant variation of dispersions of valence bands. Meanwhile, the size of spin-orbit splitting dominated by Se 4p orbitals decreases with the increase of Ti doping. Our work shows a convenient way to alter the bandgap and spin-orbit coupling in TMDCs at the low level of substitution of transition metals.

Recently, intriguing physical properties have been unraveled in anisotropic layered semiconductors, in which the in-plane electronic band structure anisotropy often originates from the low crystallographic symmetry and thus a thickness-independent character emerges. Here, we apply high-resolution angle-resolved photoemission spectroscopy to directly image the in-plane anisotropic energy bands in monoclinic gallium telluride (GaTe). Our first-principles calculations reveal the in-plane anisotropic energy band structure of GaTe measured experimentally is dominated by a strong bulk-surface interaction rather than geometric factors, surface effect and quantum confinement effect. Furthermore, accompanied by the thickness of GaTe increasing from mono- to few-layers, the strong interlayer coupling of GaTe induces direct-indirect-direct band gap transitions and the in-plane anisotropy of hole effective mass is reversed. Our results shed light on the physical origins of in-plane anisotropy of electronic structure in GaTe, paving the way for the design and device applications of nanoelectronics and optoelectronics based on anisotropic layered semiconductors., Comment: To be published in Communications Physics

In this work, SrZrO3 was used as a dopant for KNN-based lead-free piezoelectric ceramics with composition of (K0.49Na0.49Li0.02)(Nb0.8Ta0.2)O3 (denoted by KNLNT) to optimize their piezoelectric and dielectric properties. SrZrO3-modified KNLNT lead-free piezoelectric ceramics were synthesized via a conventional solid-state method. The effects of doping on crystal structure, ferroelectric properties, dielectric properties and piezoelectric properties were systematically investigated. The transformation of the crystal structures of the ceramics from orthorhombic to tetragonal has been monitored and the coexistence of orthorhombic and tetragonal phases has been identified with the range of 0.01–0.03 for the doping SrZrO3. The doping of SrZrO3 was found to be effective in reducing the grain sizes and lowering the orthorhombic–tetragonal phase transition point temperature (T O−T) and Curie temperature (T C) in SrZrO3-modified KNLNT ceramics. The optimized content of SrZrO3 is 0.02, in which the maximum d 33 of 156 pC/N can be obtained, corresponding to the disappearance of T O–T and T C of 252.5 °C.

Multiferroic ceramics consisting of barium titanate (BaTiO3, BT), bismuth ferrite (BiFeO3, BFO), and lanthanum ferrite (LaFeO3, LFO), namely (1 − x)(0.96BaTiO3–0.04BiFeO3)–xLaFeO3 (BT–BFO–xLFO, where x = 0.1–0.5), were synthesized by the sol–gel method. The crystal structure, microstructure, and dielectric, ferromagnetic, and magnetoelectric properties of the ceramics were systematically investigated. Structural analysis of BT–BFO–xLFO solid solution showed a pure perovskite structure. The Rietveld refined XRD data fitted well with an orthorhombic structure (Pbnm space group). BT–BFO–0.4LFO and BT–BFO–0.5LFO exhibited initial dielectric constants of 2114 and 1741, respectively, at 20 Hz, followed by fast decay with increasing frequency. In comparison, the BT–BFO–xLFO ceramics with x = 0.1–0.3 showed excellent stability. Remarkably improved ferromagnetic properties were obtained for BT–BFO–0.4LFO, and the remnant magnetization increased from 0.008 to 0.666 emu g−1 when x was increased from 0.1 to 0.4. The maximum value of the magnetoelectric coefficient reached 354 mV (cm−1·Oe−1) for the ceramic with x = 0.4 at 1000 kHz and 1 kOe.

Using angle-resolved photoemission spectroscopy, we study electronic structures of a Kagome metal YCr6Ge6. Band dispersions along kz direction are significant, suggesting a remarkable interlayer coupling between neighboring Kagome planes. Comparing ARPES data with first-principles calculations, we find a moderate electron correlation in this material, since band calculations must be compressed in the energy scale to reach an excellent agreement between experimental data and theoretical calculations. Moreover, as indicated by band calculations, there is a flat band in the vicinity of the Fermi level at the Γ–M–K plane in the momentum space, which could be responsible for the unusual transport behavior in YCr6Ge6.