Synthesis of the Ferroelectric Solid Solution, Pb(Zr 1-x Ti x )O 3 on a Single Substrate Using a Modified Molecular Beam
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Synthesis of the Ferroelectric Solid Solution, Pb(Zr1-xTix)O3 on a Single Substrate Using a Modified Molecular Beam Epitaxy Technique Piers S. Anderson1,2, Samuel Guerin1, Brian E. Hayden1,3, Mikael A. Khan4, Andrew J. Bell4, Yisong Han2, Ashu Pasha2, Karl R Whittle2, and Ian M. Reaney2 1 Ilika Technologies Ltd, Kenneth Dibben House, Enterprise Road, University of Southampton Science Park, Chilworth, Southampton, SO16 7NS, United Kingdom 2 Dept. of Engineering Materials, University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield, S1 3JD, United Kingdom 3 School of Chemistry, University of Southampton, Highfield Campus, Southampton, SO17 1BJ, United Kingdom 4 School of Process, Environmental and Materials Engineering, University of Leeds, Institute of Materials Research, Houldsworth Building, Leeds, LS2 9JT, United Kingdom
ABSTRACT High-throughput synthesis of the ferroelectric solid solution Pb(Zr1-xTix)O3 (PZT) on single Pt/Ti/SiO2/Si substrates was demonstrated using a modified molecular beam epitaxy (MBE) system. The PZT films exhibited a phase transition from rhombohehdral (R) to tetragonal (T) symmetry as a function of Zr:Ti ratio, across the substrate diagonal. This was consistent with the presence of a morphotropic phase boundary (MPB) at a Zr:Ti ratio of 0.64:0.36, different from the value of 0.53:0.47 observed for bulk ceramics. All points on the films exhibited ferroelectric hysteresis loops. The results demonstrate the feasibility of high-throughput MBE for deposition of complex ferroelectric oxides, and pave the way for further materials discovery, in particular Pb-free piezoceramics. INTRODUCTION There has been significant research into thin-film Pb(Zr,Ti)O3 (PZT), with deposition by methods such as sol-gel, radio-frequency (RF) magnetron sputtering, pulsed laser deposition (PLD) and metal-organic chemical vapor deposition (MOCVD)[1]. However, invariably only a single composition can be deposited during any given experiment. Here, we have used a high-throughput, modified molecular beam epitaxy (MBE) system (Figure 1) to prepare PZT with a variable Zr:Ti ratio and Pb stoichiometry, across 1 inch² Pt/Ti/SiO2/Si substrates. The system comprises two Physical Vapor Deposition (PVD) chambers under Ultra High Vacuum (UHV) conditions[2]. The PVD chambers have a plurality of off-axis sources (e-beam or Knudsen (K-cell) sources, Figure 2) for coevaporation of Pb, Zr, Ti onto a substrate in the presence of molecular O2 or atomic oxygen (produced by an RF atom source)[2].
Figure 1 – MBE-system, PVD chamber
Ti Zr e-Beam Source
K-Cell Source
K-Cell Source
Pb Figure 2 – Six-fold symmetry arrangement of e-beam and K-cell sources
Two main parameters were taken into account: the “wedge” value and the power input. Each source was independently controlled in terms of both the gradient of the deposit (or “wedge”) and the power (i.e. the rate of evaporation)[2]. The wedge was obtained by placing a shutter in a predetermined position, prior to deposition, allowing a shadow effect ont
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