Field-Induced Inversion of the Magnetoresistive Effect in the Zintl Phase Eu5+xMg18−xSi13(x=2.2)

Structural Properties of NdTiO2+xN1-x and Its Application as Photoanode

Mixed-anion inorganic compounds offer diverse functionalities as a function of the different physicochemical characteristics of the secondary anion. The quaternary metal oxynitrides, which originate from substituting oxygen anions (O^2–) in a parent oxide by nitrogen (N^3–), are encouraging candidates for photoelectrochemical (PEC) water splitting because of their suitable and adjustable narrow band gap and relative negative conduction band (CB) edge. Given the known photochemical activity of LaTiO₂N, we investigated the paramagnetic counterpart NdTiO_2+xN_1–x. The electronic structure was explored both experimentally and theoretically at the density functional theory (DFT) level. A band gap (E_g) of 2.17 eV was determined by means of ultraviolet–visible (UV–vis) spectroscopy, and a relative negative flat band potential of −0.33 V vs reversible hydrogen electrode (RHE) was proposed via Mott–Schottky measurements. ¹⁴N solid state nuclear magnetic resonance (NMR) signals from NdTiO_2+xN_1–x could not be detected, which indicates that NdTiO_2+xN_1–x is berthollide, in contrast to other structurally related metal oxynitrides. Although the bare particle-based photoanode did not exhibit a noticeable photocurrent, Nb₂O₅ and CoO_x overlayers were deposited to extract holes and activate NdTiO_2+xN_1–x. Multiple electrochemical methods were employed to understand the key features required for this metal oxynitride to fabricate photoanodes.

The structural properties of the prospective metal oxynitride NdTiO_2+xN_1−x were experimentally and theoretically investigated. The band edge positions make the compound theoretically suitable for overall photochemical water splitting.

Magnetic hyperfine field splitting in the Zintl phase Eu2Mg4Si3

Eu2Mg4Si3 ≡ (2Eu2+)(4Mg2+)(3Si4−) is an electron-precise Zintl phase. Its Hf2Co4P3-type structure contains three crystallographically independent europium sites. The divalent state of europium was manifested through 151Eu Mössbauer spectroscopy. In the paramagnetic regime (T = 78 K) the isomer shifts range from −9.16 to −11.29 mm s−1. Eu2Mg4Si3 shows complex magnetic hyperfine field splitting at T = 5.7 K with a superposition of three subspectra with magnetic hyperfine fields of 5.4 (Eu2), 20.4 (Eu1) and 22.4 (Eu3) T.