ChemInform Abstract: Crystal Chemistry and Thermal Behavior in the La(Cr,Ni)O3 Perovskite System.

Abstract

Crystal Chemistry and Thermal Behavior in the La(Cr,Ni)O3 Perovskite System. -The rhombohedral perovskite LaNiO3 decomposes into La4Ni3O10 and NiO above 825 • C both in air and in oxygen; above 1196 • C ( air) or 1291 • C (O2) La2NiO4 is formed besides NiO. Orthorhombic LaCrO3 transforms at 271 • C into a rhombohedral high-temp. phase, which is stable up to 1550 • C. The La(Cr,Ni) O3 systems show no miscibility gap at room temp. as well as at higher temperature. Samples containing up to 60% LaNiO3 have the orthorhombic LaCrO3-type structure, while those containing ≥ 70 mol% LaNiO3 are rhombohedral. The orthorhombic-to-rhombohedral phase transition temp. of LaCrO3 increases with increasing substitution of Ni for Cr and reaches a maximum value of 346 • C at 20-30 mol% LaNiO3. The thermal expansion coefficients of the rhombohedral high-temp. phases are higher than those of the orthorhombic low-temp. phases. -(HOEFER, H. E.; KOCK, W. F.; J.

Thermodynamic Assessment of the La-Cr-O System

“…Existing experimental data of lanthanum chromite perovskite structure, [33][34][35][36][37][38][39][40][41][42][43][44][45] thermodynamics, [30,[33][34][35]43,[46][47][48][49][50][51][52][53] phase stability, [54] and nonstoichiometry [55,56] along with the investigation techniques used are listed in Table 1.…”

“…[20,[33][34][35][36][37][38][39][40][41][42] Both the rhombohedral and orthorhombic forms of LaCrO 3 are slight distortions of the perovskite crystal structure. The perovskite structure is primitive cubic and with the formula ABX 3 and has an A atom at the unit cell origin, (0,0,0), a B atom at the body-centered position (½, ½, ½), and three X atoms at the face-centered positions, (½, ½, 0; ½, 0, ½, ½, 0, ½, ½).…”

“…A transformation from rhombohedral to cubic structure at a temperature close to 1300 K was reported by Ruiz et al [37] and Momin et al, [41] whereas Coutures et al [20] reported 1923 K using high-temperature X-ray diffraction (HT-XRD), in agreement with Berjoan [19] (1923 ± 20 K) using dilatometry. Berjoan [19] further reported prevailing of the cubic structure at 2173 K. On the other hand Geller and Basic and Applied Research: Section I Raccah [38] as well as Höfer and Kock [34] did not observe the rhombohedral to cubic transition up to T = 1873 K and T = 1823 K respectively using differential thermal analysis (DTA).…”

“…The heat capacities of LaCrO 3 were measured by Korobeinikova and Reznitskii [33] from 340 to 900 K using adiabatic calorimetry, Höfer and Kock [34] (480-610 K) and Satoh et al [45] (150-450 K) using DSC, Satoh et al [45] (77-280 K) using alternating current calorimetry, Sakai et al [35] (100-1000 K) using laser-flash calorimetry, and Sakai and Stølen [43] (272-1000 K) using adiabatic shield calorimetry. Enthalpy increments of LaCrO 3 at 1090 and 1350 K were measured by Suponitskii [30] using a high-temperature heatconducting calorimeter.…”

“…Enthalpy increments of LaCrO 3 at 1090 and 1350 K were measured by Suponitskii [30] using a high-temperature heatconducting calorimeter. [46] Standard entropy S LaCrO3 298 K ¼ 109:2 J mol À1 K À1 this work, calculated Gibbs energy of formation by 3 4 [49] solid oxide electrolyte-emf T ¼ 1273 K D G ¼ À42:29 AE 0:38 kJ mol À1 [52] CaF 2 -based emf T ¼ 2100 K D G ¼ À79:52 kJ mol À1 this work, calculated T ¼ 2100 K D G ¼ À78:9 AE 1:1 kJ mol À1 [53] Knudsen mass spectrometry D G ¼ À72:403 À 0:0034T ðkJ mol À1 Þ; 1273 À 2673 K this work, calculated D G ¼ À44:45 þ 0:002115T AE 0:4 ðkJ mol À1 Þ; 855 À 1073 K [50] CaF 2 -based emf D G ¼ À94:758 þ 0:08530T ðkJ mol À1 Þ; 700 À 885 K [51] CaF 2 -based emf Enthalpy increments H À H 298 K ; kJ mol À1 T ¼ 1090 K 98.19, this work, calculated 94.4 [30] HT(high temperature)-calorimetry T ¼ 1350 K 133.05 this work, calculated 139.2 [30] HT-calorimetry Activity of Cr 2 O 3 in LaCrO 3 T ¼ 2100 K a Cr2O3 ¼ 1:11 Â 10 À4 this work, calculated T ¼ 2100 K Transition temperature, K 540, this work, calculated 503-583 [33] adiabatic calorimetry 544 ± 1 [34] (a) DTA, DSC, thermogravimetry, dilatometry 536 [35] (a) adiabatic shield calorimetry, HT-XRD (air and vacuum) 563 ± 5 [36] DTA, dilatometry, HT-XRD, HT-microscopy, HT-X-ray photography 550 [37] HT-XRD 528-533 [38] (a) HT-XRD 533 ± 3 [38] (a) DTA 543 [39] XRD 533 [20] HT-XRD 540 ± 2 [40] (a) HT-XRD, DSC 533 ± 5 [40] (a) HT-XRD, dilatometry 545 [41] heating, DSC 535 [41] cooling DSC 550 [41] HT-XRD 523 [42] (a) starting transition, simultaneous DSC-XRD 541 [42] (a) completed transition, simultaneous DSC-XRD 533 [43] estimated from neutron powder diffraction 509 [44] DSC, XRD Enthalpy change of transition, J mol -1 340, this work, calculated 502.08 ± 41.84 at 503-583 K [33] calculated from adiabatic calorimetry 277 at 544 ± 1 K [34] (a) DSC 403.25 at 536 …”