Synthesis Attempt and Structural Studies of Novel A₂CeWO₆ Double Perovskites (A²⁺ = Ba, Ca) in and outside of Ambient Conditions

Abstract

This comprehensive work showcases two novel, rock-salt-type minerals in the form of amphoteric cerium–tungstate double perovskite and ilmenite powders created via a high-temperature solid-state reaction in inert gases. The presented studies have fundamental meaning and will mainly focus on a detailed synthesis description of undoped structures, researching their possible polymorphism in various conditions and hinting at some nontrivial physicochemical properties like charge transfer for upcoming optical studies after eventual doping with selectively chosen rare-earth ions. The formerly mentioned, targeted A 2 BB′X 6 group of compounds contains mainly divalent alkali cations in the form of XII A = Ba 2+ , Ca 2+ sharing, here, oxygen-arranged clusters ( II X = O 2– ) with purposely selected central ions from f-block VI B = Ce 4/3+ and d-block VI B′ = W 4/5/6+ since together they often possess some exotic properties that could be tuned and implemented into futuristic equipment like sensors or energy converters. Techniques like powder XRD, XPS, XAS, EPR, Raman, and FTIR spectroscopies alongside DSC and TG were involved with an intent to thoroughly describe any possible changes within these materials. Mainly, to have a full prospect of any desirable or undesirable phenomena before diving into more complicated subjects like: energy or charge transfer in low temperatures; to reveal whether or not the huge angular tilting generates large enough dislocations within the material’s unit cell to change its initial properties; or if temperature and pressure stimuli are responsible for any phase transitions and eventual, irreversible decomposition.

Studies on the Structure and Optical Properties of BaSrMgWO₆ Thin Films Deposited by A Spin Coating Method

“…The best fit in the deconvolution of XPS Ba 3d was obtained for 61.9 % for Ba 2+ species in BaSrMgWO6, 25.4% for Ba 2+ in under-stoichiometric phases of type Ba2-(x+y) SrxMgyWO5 and 12.7 % for surfaces oxides, as we expected (Table 3) [41][42][43]. The Sr 3d XPS high resolution spectrum was fitted with three doublets, restricted by an equal FWHM of 2 eV; a fixed doublet separation of 1.7 eV (spin orbit splitting) and an area ratio of d5/2 to d3/2 of 3:2 [25,43].…”

Synthesis and Properties of the Ba2PrWO6 Double Perovskite

“…The EPR spectrum of BPW recorded at 3 K is presented in Figure a. Since Pr 3+ ions with 4f 2 electron configuration cannot be detected in our conventional EPR setup, we expected to detect mainly an anisotropic (C 2h local symmetry) powder spectrum of Pr 4+ (4f 1 ) , ions, similar to that of the isoelectronic Ce 3+ observed previously in BCW, which would be visible only at cryogenic temperatures. Instead, the spectrum is dominated by an isotropic paramagnetic signal that persists up to RT (red line in Figure a).…”

“…Some peaks are so weak that their pressure dependence cannot be followed in the whole rangethis concerns especially the debatable ones related to PrO 2– x defects (see Figure S6). Phase transitions at higher pressures cannot be excluded, but up to 20 GPa, the material is quite stable as hysteresis during pressure release is not higher than 2 GPa, comparable to BCW from our previous work …”

“…Phase transitions at higher pressures cannot be excluded, but up to 20 GPa, the material is quite stable as hysteresis during pressure release is not higher than 2 GPa, comparable to BCW from our previous work. 30 3.6. Material Stability at High Temperatures.…”

“…15,16 Perovskites gained great scientific and technological interest as microwave dielectrics, 2,17,18 piezoelectric sensors, 2,3,19 electrodes for fuel cells, 20−22 magnetic memory components, 23 catalysts, 24−26 or solar cell materials. 27−29 Recently, we have added a new DP, Ba 2 CeWO 6 (BCW), 30 to the about thousand DP oxides listed in ref 1, which were synthesized up to 2015. Now, we add another new DP to the list�Ba 2 PrWO 6 (BPW).…”