Thermal analysis of rare earth gallates and aluminates

Abstract

Dilatometry, high-temperature x-ray diffraction, differential thermal analysis, and differential scanning calorimetry have been performed on LaGaO3, NdGaO3, PrGaO3, SmAlO3, and LaAlO3 single crystals grown by the Czochralski technique. First order phase transitions have been located at 145 °C for LaGaO3 and 785 °C for SmAlO3, and Ai/ has been measured for the LaGaO3 transition. Second order transitions have been identified for LaGaO3, PrGaO3, NdGaO3, and LaAlO3. The usefulness of these compounds as substrates for high temperature superconducting films is discussed in terms of thermal expansion matching.

Defects in Detwinned LaGaO3Substrates

“…First-order phase transition, from orthorhombic to rhombohedral structure, was observed in LaGaO3 and SmΑlO3 at 150°C and 7850C, respectively. In turn, second-order phase transition occurs at 11800C for LaGaO3 , 9500C for NdGaO 3 , 8700C for PrGaO3 and around 5000C for LaΑlO3 [3].…”

“…Lanthanum, neodymium and praseodymium gallates [1,2] have often been expected as substrate materials for HTSC epí-taxy mainly because of their attractive dielectric properties (low ε and tan δ) and low lattice mismatches, both at deposition and application temperatures. The most crucial problem in application of these materials as substrates for the epitaxy is the existence of the structural phase transitions [3] leading to the twinning and surface roughening [4]. First-order phase transition, from orthorhombic to rhombohedral structure, was observed in LaGaO3 and SmΑlO3 at 150°C and 7850C, respectively.…”

X-Ray Diffraction Investigations of NdGaO3Single Crystal

“…The first of authors [3] reported that twinning is correlated with second-order phase transition. Many other authors regard unsuitable thermal gradients as reason for the formation of twins [1,4].…”

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“…The phase transition is the most serious drawback of many lanthanide gallates and aluminates 5 for it can cause formation of twins and roughness of the substrate surface6. We have previously investigated the Lal-,Nd.GaO 3 Lal_,Pr.GaO 3 systems 7 "8 and found crystals with the lattice parameters suitable as substrates for High Temperature Superconductors (HTSc) epitaxy.…”