Growth of Laser Ablated YBa₂Cu₃O₇Thin Films Epitaxied on (100)MgO: Influence of In-Plane Misorientations on Low and High Frequency Properties

Abstract

Tle graphoepitaxial growth of c-axis YΒa2Cu3O7 laser ablated thin films on (100)MgO induces a competition between two main in-plane orientations due to the large lattice mismatch: (100) YΒa2Cu3O7 || (100) MgO, c10 notation or (I 10) YΒa2 Cu3O7 || (100) MgO, c145 notation. The ratio of c┴45 /c┴0 in-plane orientations (η), measured by X-ray diffraction φ scans, is ranging from 0.2% to 49.7% for the films reported here. Their crystalline qualities were compared on the basis of rocking curves (Δθ), electron channelinng patterns and reflection high energy electron diffraction diagrams. The coexistence of c┴ 0 a n d G 1 4 5 d o m a i n s c r e a t e s h i g h a n g l e g r a i n b o u n d a r i e s . N o degradation of Τc , residual resistance ratio (RRR) or ΔTc is observed when η increases. In contrast, a strong correlation between microwave losses characterized by surface resistance (Rs at 10 GHz and 77 K), inductive losses S(χ") (surface of the χ" peak obtained in a.c. susccptibility at 119 Hz) and η was clearly evidenced. A minimum of losses was found for η between 3 and 6% suggesting the necessity of a low quantity of high angle grain boundaries for films optimization. Finally, some specific processes carried out recently in order to try to efficiently control η, then Rs are discussed.PACS numbers: 68.55. Jk, 73.25.+i 1. Introduction The control of the growtl of ligl quality epitaxial thin fllms of HTSC materials opens the way to a number of applications, specially in the field of microwave devices. however, working at high frequencies implies additional requirements on the dielectric properties of the substrates and, in this aspect, (100)MgO single crystal is one of the most popular. Unfortnnately, this material presents an important misfit with HTSC, meaning severe limitations in the mechanism of heteroepitaxial growth. In this paper, we will focus on the growth of YΒa2Cu3O7 (YBCO) on (100)MgO using pulsed laser deposition, thc specific defects of such films and their implication on the surface resistance RS wlich is the pertinent parameter for any microwave applications.

Fluorination Under NF3Flow of Oxygen Deficient YBa2Cu3OxThin Films Deposited on Various Types of Substrate

“…It was attributed to the influence of the nature of the substrate on the thin fllm growth and then to the nature of the grain boundaries [10]. Indeed, the films deposited on (100)MgO in most cases contain an array of high angle grain boundaries [12]. This is not the case for the films deposited on (100)SrTiO3 for which the mismatch is considerably smaller.…”