Origin of Enhanced Electromechanical Coupling in (Yb,Al)N Nitride Alloys

TL;DR

This study investigates how alloying YbN into AlN enhances electromechanical coupling through experimental and computational methods, revealing structural and compositional factors that influence this property.

Contribution

It provides new insights into the mechanisms behind enhanced electromechanical coupling in (Yb,Al)N alloys, combining experimental results with first-principles calculations.

Findings

Alloying YbN softens AlN mechanically.

Electromechanical coupling increases by up to 270%.

Yb-Yb pair interactions influence structural flexibility.

Abstract

Our experiments demonstrate that alloying the cubic-phase YbN into the wurtzite-phase AlN results in clear mechanical softening and enhanced electromechanical coupling of AlN. First-principle calculations reproduce experimental results well, and predict a maximum 270% increase in electromechanical coupling coefficient caused by (1) an enhanced piezoelectric response induced by the local strain of Yb ions and (2) a structural flexibility of the (Yb,Al)N alloy. Extensive calculations suggest that the substitutional neighbor Yb-Yb pairs in wurtzite AlN are energetically stable along $c$ axis, and avoid forming on the basal plane of wurtzite structure due to the repulsion between them, which explains that (Yb,Al)N films with high Yb concentrations are difficult to fabricate in our sputtering experiments. Moreover, the neighbor Yb-Yb pair interactions also promote structural flexibility of (Yb,Al)N, and are considered a cause for mechanical softening of (Yb,Al)N.