Indentation fracture of lead magnesium niobate-based multilayer composite structures
- PDF / 1,388,682 Bytes
- 9 Pages / 593.28 x 841.68 pts Page_size
- 74 Downloads / 218 Views
I. INTRODUCTION Perovskite lead magnesium niobate, Pb(Mg1/3Nb2/3)O3 (PMN), was first synthesized in the late 1950s.1'2 Since then, the dielectric,3 optical,3"5 electrostrictive,6 and microstructural 7 properties of PMN-based materials have been investigated. A study8 of the dielectric properties of PMN versus temperature has shown that these materials exhibit a high and broad dielectric maxima associated with its diffuse paraelectric to ferroelectric phase transition. The anomalously high dielectric constant and broad permittivities and subsequent electrostrictive strains have made them promising candidates for actuator and capacitor applications. Perovskite PbTiO3 (PT) is a well-known ordered ferroelectric which exhibits a sharp first order phase transition upon cooling at 490 °C from a cubic paraelectric phase transition to a tetragonal ferroelectric. Suitably chosen compositions in the PMN-PT family allow one to tailor the dielectric properties and may exhibit electrostrictive strains much larger than other perovskites, such as barium titanate (BaTiO3),9 and in the range of piezoelectric materials such as lead zirconate titanate (PZT)10 ceramics. The high dielectric and piezoelectric constants of PMN and PMN-PT make them ideal candidates for electrostrictive strain applications,11"16 electro-optic applications,17'18 and dielectric/pyroelectric bolometers.18 The electrostrictive PMN-PT relaxor ferroelectric materials offer advantages over known piezoelectric materials, since they exhibit improved positional reproducibility (no voltage aging), and poling is not required. Other advantages of electrostrictive actuators over their electromagnetic competitors include lower consumption and heat generation and significant size reduction. Because of these advantages, electrostrictive materials are good candidates for solid state positioners J. Mater. Res., Vol. 5, No. 3, Mar 1990
http://journals.cambridge.org
Downloaded: 17 Mar 2015
and motion actuators. Both these applications benefit from multilayer design which allows for high internal field under low voltage and produces high strain with fast response time. It was shown19 that the multilayer design using PMN-based ceramic could achieve strain levels of 8.7 x 10~4, with forces as high as 3.5 x 107 N/m 2 , with a 100 ^.sec response time and a 70% electromechanical coupling factor under a 1 x 106 V/m field. For positioning and actuating applications these devices must operate under mechanical loads of various types. Electrostrictive actuators could operate under high compressive stresses (0.1 GPa) and still produce strains up to 10~3 with a very fast response.10 The purpose of this paper was to investigate the fracture behavior of PMN multilayer structures. The strength indentation technique20"22 was used to determine their fracture strength and toughness.
II. BACKGROUND Indentation fracture has been established as an important technique for investigating the mechanical properties of ceramic materials.20"26 Controlled indentations provide a means of introducing crac
Data Loading...
