High-Throughput Selection and Experimental Realization of Two New Ce-Based Nitride Perovskites: CeMoN3 and CeWN3

Abstract

Nitride perovskites have only been experimentally realized in very few cases despite the widespread existence and commercial importance of perovskite materials. From oxide perovskites used in ultrasonics to halide perovskites that have revolutionized the photovoltaics industry, the discovery of new perovskite materials has historically impacted a wide number of fields. Here, we add two new perovskites, CeWN₃ and CeMoN₃, to the list of experimentally realized perovskite nitrides using high-throughput computational screening and subsequent high-throughput thin film growth techniques. Candidate compositions are first down-selected using a tolerance factor and then thermochemical stability. A novel competing fluorite-family phase is identified for both material systems, which we hypothesize is a transient intermediate phase that crystallizes during the evolution from an amorphous material to a stable perovskite. Different processing routes to overcome the competing fluorite phase and obtain phase-pure nitride perovskites are demonstrated for the CeMoN_3-x and CeWN_3-x material systems, which provide a starting point for the development of future nitride perovskites. Additionally, we find that these new perovskite phases have interesting low-temperature magnetic behavior: CeMoN_3-x orders antiferromagnetically below T _N ≈ 8 K with indications of strong magnetic frustration, while CeWN_3-x exhibits no long-range order down to T = 2 K but has strong antiferromagnetic correlations. This work demonstrates the importance and effectiveness of using high-throughput techniques, both computational and experimental: they are integral to optimize the process of realizing two entirely novel nitride perovskites.

Figure 1

Lab XRD of different stoichiometries in the (Ce,Mo)N system (A) and the (Ce,W)N system (B) showing the coexisting fluorite family near the perovskite 1:1 cation ratio. The white boxes highlight the coexistence of the highest intensity perovskite and highest intensity fluorite diffraction peaks. Reference peaks are based off of the cubic prototype of the perovskite structure.

Figure 2

Computed ternary phase diagrams for CeMoN₃ (A) and CeWN₃ (B) showing possible competing phases for each chemistry studied. ΔH_d is shown for the stability-defining reaction for each perovskite phase: (1/4)Ce₄N₇ + (3/4)MoN + (1/4)MoN₂ → CeMoN₃ and CeN + WN₂ → CeWN₃. Blue circles indicate thermodynamically stable phases, and red triangles indicate thermodynamically unstable phases.

Figure 3

(A) Lab XRD of a single point on a (Ce,Mo)N_3–x film with nominal composition Ce_0.66Mo_0.34N_3–x by XRF annealed at 1173 K for progressive holds in a flowing N₂ atmosphere. A vertical offset is applied to separate the data. (B) LeBail fit in space group Pm3̅m of lab XRD data of the same (Ce,Mo)N_3–x film with nominal composition Ce_0.61Mo_0.39N_3–x annealed at 1173 K for 10 min. wR = 8.68%, and goodness of fit (GOF) = 10.32.

Figure 4

(A) BF STEM cross section showing a very fine grain size and (B) AES depth profile of light element signals of a CeMoN_3–x film with nominal composition Ce_0.54Mo_0.46N_3–x by XRF after annealing for 10 min in flowing N₂. Only the surface layer of the sample contains significant oxygen; the majority of the sample has very low oxygen signal, indicating that the change during annealing is not due to incorporation of oxygen but to crystallization kinetics.

Figure 5

(A) Lab XRD of (Ce,W)N films grown at 900 K showing a phase-pure perovskite near and slightly above the 1:1 Ce:W ratio. At compositions with lower Ce content, W-rich phases formed. A peak associated with the substrate has been removed by removing a range of χ from the integration after it did not appear in electron diffraction in Figure S2 in the Supporting Information. (B) LeBail fit in space group Pm3̅m of the lab XRD pattern of the composition Ce_0.5W_0.5N_3–x in panel A. The 2θ region around a peak associated with the Si substrate has been removed. wR = 9.38%, and goodness of fit (GOF) = 9.85.

Figure 6

(A) BF STEM cross section of a CeWN_3–x film with nominal composition Ce_0.51W_0.49N_3–x by XRF showing columnar microstructure within the film. The dark layer at the top is Pt from sample preparation. (B) AES of the same CeWN_3–x film showing increasing oxygen content near the surface of the film, presumably because of prolonged exposure to oxygen in the atmosphere. Two scans were performed as the first did not penetrate the full film depth, which caused a spike in oxygen measured at the newly created surface.

Figure 7

Magnetic properties of CeWN_3–x and CeMoN_3–x. (A) Low-field zero field cooled (ZFC) and field cooled (FC) susceptibility of CeWN_3–x measured in an applied field of μ₀H = 0.005 T. Inset: Inverse susceptibility measured in an applied field of μ₀H = 5 T with a diamagnetic correction of χ₀ = −3.91 × 10^–4 emu/Oe. Data in the range T = 237–256 K are masked out because of instrumental artifacts. The line is a Curie–Weiss fit from T = 150 to T = 300 K. (B) Magnetization of CeWN_3–x as a function of applied field at T = 2 K and T = 10 K. (C) Low-field ZFC and FC susceptibility of CeMoN_3–x measured in applied fields of μ₀H = 0.005–0.5 T. Inset: Inverse susceptibility measured in an applied field of μ₀H = 5 T with a diamagnetic correction of χ₀ = −4.33 × 10^–4 emu/Oe. Data in the range T = 238–263 K are masked out because of instrumental artifacts. The line is a Curie–Weiss fit from T = 150 to T = 300 K. (D) Magnetization of CeMoN_3–x as a function of applied field at T = 2 K and T = 10 K.