Phase stability of epitaxial KTa_xNb_1−xO₃ thin films deposited by metalorganic chemical vapor deposition

Abstract

The phase stability of epitaxial KTaxNb1−xO3 (0 ≤ x ≤ 1) thin films, with compositions over the entire solid solution range, was investigated. KTaxNb1−xO3 thin films were deposited on (100) MgAl2O4 substrates by metalorganic chemical vapor deposition. Films with compositions x ≤ 0.30 were orthorhombic, as determined by x-ray diffraction. Dielectric measurements at room temperature indicated the presence of morphotropic phase boundaries at x = 0.30 and at x = 0.74. Temperature-dependent measurements of the dielectric constant for KNbO3 from 80 to 800 K indicated three structural phase transitions at 710, 520, and 240 K. For intermediate compositions, a decrease in the Curie and tetragonal–orthorhombic transition temperatures was observed with increasing Ta atomic percent, similar to the bulk phase equilibrium. In contrast to bulk materials, an increase in the orthorhombic–rhombohedral transition temperature with increasing x was observed for the films, resulting in the stabilization of a rhombohedral phase at room temperature for compositions 0.45 ≤ x ≤ 0.73. Differences between the phase stability for the thin films and bulk were attributed to lattice misfit strain.

Epitaxially grown ferroelectric thin films for agile devices

“…These temperatures of phase transitions are close to data reported for KNbO 3 single-crystals [41,130]. Nevertheless, the transition temperatures are slightly lower for our film than for some samples reported by other groups [87,93,131,132]. The difference can be due to strain or, more likely, to grains size.…”

“…Various methods were also carried out for KTN thin films deposition, like liquid-phase epitaxy [85], MOCVD [86,87], sol-gel methods [51][52][53]88] (including polymeric precursors [54,55]), radio frequency sputtering [56,89] and PLD [39,40,46,[90][91][92][93][94][95]. Most of these studies highlighted the difficulty to preserve the relationship between metal atoms according to the pseudo-binary diagram established for the synthesis of KTN single-crystals [45,85,96] or ceramics [16,44,97].…”

Growth and characterization of barium-doped potassium tantalate crystals

“…The growth of barium-doped KT was already reported from our laboratory [10,11], but to our knowledge there are no reports on the investigations on the growth of bulk homogeneously-doped KT:Ba crystals. The investigations on the growth of KTN and KNTN thin films have been reported by several authors [12][13][14][15][16][17][18]. For the practical realization of optical devices such as waveguides and microresonators wide area (5 Â 5 mm 2 ) with flat as grown epilayers of uniform composition are needed.…”

Low-Temperature Epitaxy of KTaO[sub 3] and KNbO[sub 3] Films

“…3 Alloying with niobium, the cubic phase of KTa 1−x Nb x O 3 ͑KTN͒ is a good candidate material for electro-optic applications, such as band filters, light modulators, and IR detectors, due to its large quadratic electro-optic coefficient and photorefractive effect. 4 Because bulk single crystals of KTaO 3 and KTN are difficult and expensive to grow, attention has been focused on the growth of epitaxial films.…”

“…2,4,5 These processes require temperatures in excess of 650°C either during deposition or for postdeposition calcination. Alternatively, epitaxial KTaO 3 films can be grown by a low temperature ͑Ͻ200°C͒ solution technique known as hydrothermal epitaxy that utilizes aqueous chemical reactions to form heteroepitaxial thin films.…”