Thermal Analysis of High Entropy Rare Earth Oxides

Abstract

Phase transformations in multicomponent rare earth sesquioxides were studied by splat quenching from the melt, high-temperature differential thermal analysis and synchrotron X-ray diffraction on laser-heated samples. Three compositions were prepared by the solution combustion method: (La,Sm,Dy,Er,RE)2O3, where all oxides are in equimolar ratios and RE is Nd or Gd or Y. After annealing at 800 °C, all powders contained mainly a phase of C-type bixbyite structure. After laser melting, all samples were quenched in a single-phase monoclinic B-type structure. Thermal analysis indicated three reversible phase transitions in the range 1900–2400 °C, assigned as transformations into A, H, and X rare earth sesquioxides structure types. Unit cell volumes and volume changes on C-B, B-A, and H-X transformations were measured by X-ray diffraction and consistent with the trend in pure rare earth sesquioxides. The formation of single-phase solid solutions was predicted by Calphad calculations. The melting point was determined for the (La,Sm,Dy,Er,Nd)2O3 sample as 2456 ± 12 °C, which is higher than for any of constituent oxides. An increase in melting temperature is probably related to nonideal mixing in the solid and/or the melt and prompts future investigation of the liquidus surface in Sm2O3-Dy2O3, Sm2O3-Er2O3, and Dy2O3-Er2O3 systems.

Electrodeposition and Characterization of Lanthanide Elements on Carbon Sheets

“…Lanthanide (Ln) elements have been studied extensively in diverse industrial applications of magnets, high-k gate dielectrics, display materials, catalysts, and batteries [1][2][3][4][5][6]. For recycling used Ln materials, various recovery methods for Ln elements have also been demonstrated [7][8][9][10][11][12][13].…”

Energetics and structure of the B‐type solid solution in the Nd2O3–Y2O3 system

“…Understanding the phase relations in RE oxides thus becomes very important to improve and optimize the performance of advanced multicomponent systems. [4][5][6] Pure and mixed RE sesquioxides exist in different polymorphic forms, the stability of which is mainly governed by cation radii, temperature, and pressure. A-type (P 3m1), B-type (C2/m), and C-type (𝐼𝑎 3) structures are favored below about 2300 K (Figure 1).…”

“…Recent research on alloying and doping with RE elements demonstrates their importance as advanced multicomponent systems, sometimes called high entropy materials. Understanding the phase relations in RE oxides thus becomes very important to improve and optimize the performance of advanced multicomponent systems 4–6 …”

Special Issue: Thermal Analysis of Materials

“…Another set of papers deals with the development of new or application-specific approaches, namely laser interferometry techniques for high precision measurements on non-standard samples, such as composite truss structures [ 5 ]; measurements of high temperature compressive creep in spark plasma sintering apparatuses [ 6 ]; measurements of the density of liquid oxides with aero-acoustic levitators [ 7 ]; and the simultaneous estimation of thermal conductivity and heat capacity in metal alloys [ 8 ].The range of materials covered includes polymers [ 9 , 10 ]; natural complex inorganic materials, such as natural sorbents [ 1 ] and industrial-grade thermal insulation [ 4 ]; single phase ceramic materials, such as spinel MgAl 2 O 4 [ 11 ], rare earth sesquioxides [ 12 ], and double perovskite cobaltites [ 13 ]; metals, alloys, and intermetallic compounds [ 8 , 14 , 15 , 16 ].…”

“…These heating rates are relevant to welding and laser melting processing but too fast for conventional differential scanning calorimeters and too slow for fast-scanning chip calorimetry. Examples of the applications of thermal analysis and calorimetry techniques to obtain thermodynamic data vary from measurements of enthalpies of water adsorption on defect spinel surfaces [ 11 ] to phase transformation enthalpies and entropies above 2000 °C in rare earth oxides [ 12 ].…”