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Recently, nanolaminated ternary carbides have attracted immense interest due to the concomitant presence of both ceramic and metallic properties. Here, we grow nanolaminate Ti3AlC2 thin films by pulsed laser deposition on c-axis-oriented sapphire substrates and, surprisingly, the films are found to be highly oriented along the (103) axis normal to the film plane, rather than the (000l) orientation. Multiple characterization techniques are employed to explore the structural and chemical quality of these films, the electrical and optical properties, and the device functionalities. The 80-nm thick Ti3AlC2 film is highly conducting at room temperature, with a resistivity of about 50 µΩ cm and a very-low-temperature coefficient of resistivity. The ultrathin (2 nm) Ti3AlC2 film has fairly good optical transparency (∼70%) and high conductivity (sheet resistance ∼735 Ω/sq) at room temperature. Scanning tunneling microscopy reveals the metallic characteristics (finite density of states at the Fermi level) at room temperature. The metal-semiconductor junction of the p-type Ti3AlC2 film and n-Si show the expected rectification (diode) characteristics, in contrast to the ohmic contact behavior in the case of Ti3AlC2/p-Si. A triboelectric-nanogenerator-based touch-sensing device, comprising of the Ti3AlC2 film, shows a very impressive peak-to-peak open-circuit output voltage (∼80 V). These observations reveal that pulsed laser deposited Ti3AlC2 thin films have excellent potential for applications in multiple domains, such as bottom electrodes, resistors for high-precision measurements, Schottky diodes, ohmic contacts, fairly transparent ultrathin conductors, and next-generation biomechanical touch sensors for energy harvesting.

Here, we investigate in detail the low temperature structural and physical properties of the trilayer nickelates R4Ni3O10 (R = La, Pr and Nd) using resistivity, thermopower, thermal conductivity, specific heat, highresolution synchrotron powder X-ray diffraction, and thermal expansion experiments. We show that all three compounds crystallize with a monoclinic symmetry (space group P 21/a, Z = 4), and undergo a metal-to-metal transition (MMT) near TMMT = 135 K (La), 156 K (Pr) and 160 K (Nd). Upon cooling below MMT, the lattice parameters in each case show a distinct anomaly at TMMT, however, without any lowering of the lattice symmetry. Unambiguous signatures of MMT are also observed in magnetic and thermal measurements, suggesting that there is a strong coupling between the electronic, magnetic and structural degrees of freedom in these nickelates. Analysis of thermal expansion yields hydrostatic pressure dependence of MMT in close agreement with previous experimental results. In Pr4Ni3O10, we show that the 9-fold coordinated Pr 3+ ions in the rocksalt (RS) layers have a crystal field (CF) split doublet ground state with possible antiferromagnetic ordering near 5 K. In contrast to this, the Pr 3+ ions in the perovskite-block (PB) layers with a 12-fold coordination seems to exhibit a non-magnetic singlet ground state. In Nd4Ni3O10, on the other hand, the CF ground state of Nd 3+ ions in both RS and PB layers is a Kramers doublet. The heat capacity of Nd4Ni3O10 shows a pronounced Schottky-like anomaly near T = 35 K; and, an upturn below 10 K due to the presence of short-range correlations between the Nd moments. However, no signs of long-range ordering could be found down to 2 K despite a sizeable value of θp ∼ −40 K. The strongly suppressed magnetic long-range ordering in both R = Pr and Nd suggests the presence of strong magnetic frustration in these compounds. The low-temperature resistivity shows a − √ T dependence, and the electronic term in the specific heat of Nd4Ni3O10 is falsely inflated due to the overwhelming Schottky contribution. These observations rule out the alleged heavy fermion behavior recently reported for Nd4Ni3O10.

The pyrochlore iridates (Eu1-xBix)2Ir2O7 (0 ≤ x ≤ 1) undergo an anomalous negative lattice expansion (NLE) for small Bi-doping (x < 0.035) (region I) and a normal lattice expansion for x > 0.1 (region II); this is accompanied by a transition from an insulating (and magnetically ordered) to a metallic (and with no magnetic ordering) ground state. Here, we investigate (Eu1-xBix)2Ir2O7(0 x 1) using hard x-ray photoemission spectroscopy (HAXPES) and x-ray absorption fine structure (XAFS) spectroscopy. By analyzing the Eu-L3, Ir-L3 and Bi-L2 & L3 edges XANES spectra and Eu-3d core-level XPS spectra, we show that the metal cations retain their nominal valence, namely, Ir4+, Bi3+ and Eu3+, respectively, throughout the series. The Ir-4f and Bi-4f core-level XPS spectra consist of screened and unscreened doublets. The unscreened component is dominant In the insulating range x 0.035), but in the metallic region, x ‒ 0.1), the screened component dominates the spectra. The Eu-3d core-level spectra remain invariant under Bi doping. The EXAFS data show that the coordination around the Ir remains well preserved throughout the series. The evolution of the valence band spectra (VBS) near the Fermi energy with increasing Bi doping indicates the presence of strong Ir(5d)-Bi(6p) hybridization which drives the metal-to-insulator transition.