Growth of crack free Nd₂Ti₂O₇ thin films using La_0.7Sr_0.3MnO_3±δ as a template layer for high temperature pyroelectric applications

Abstract

Neodymium titanate (${\mathrm{Nd}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$) is a ferroelectric as well as a pyroelectric material with a transition temperature of 1480 °C. Hence, ${\mathrm{Nd}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ offers potential to be utilized as high temperature pyroelectric sensor in both bulk and thin film form. In this work, bulk ${\mathrm{Nd}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ powders were synthesized using solid state reaction method, which were later pressed into the pellets. Later, thin films of ${\mathrm{Nd}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ were deposited on commercially available platinized(111) silicon and Si(100) substrates via pulsed laser deposition technique. The huge c/a ratio (∼1.695) and the thermal expansion mismatch with most of the commonly used substrates like silicon and platinized silicon, results into crack formation in ${\mathrm{Nd}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ thin films. Crack formation on ${\mathrm{Nd}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ thin film, which deteriorates pyroelectric property of ${\mathrm{Nd}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ film, was suppressed by the introduction of ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}\mathrm{M}\mathrm{n}{\mathrm{O}}_{3\pm \mathrm{\delta }}$ buffer layer between the film and substrate. The calculated value of thermal expansion coefficient of ${\mathrm{Nd}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ is 2.86 × 10⁻⁵ °C⁻¹. Moreover, thermally generated strain between ${\mathrm{Nd}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ film and platinum substrate was found to be around 2%. The piezoresponse force microscopy experiment confirms the existence of ferroelectric domains in the film. Pyroelectric coefficient (p) calculated from the pyrocurrent studies was estimated around 3.52 and 13.6 μC/m²K in the bulk and thin film, respectively.

Keywords:

• Neodymium titanate
• LSMO
• pyroelectric coefficient
• atomic force microscopy (AFM)
• piezoresponse force microscopy (PFM)
• pulsed lase deposition (PLD)

Additional information

Funding

We express our gratitude to DST-SERB (Project No. EMR/2017/003159) for their support and help. The author, Manish Chandra Joshi, would like to thank MHRD for financial assistance.