Sporting a revivified sound as well as a sultry new hair style, Katherine McPhee makes a significant career advance on her sophomore album Unbroken. Collaborating with such notables as Ingrid Michaelson, Rachael Yamagata and Paul Cole, McPhee probes the thrills and pitfalls of love with a clear-eyed maturity. The thoughtful, piano-centered “Surrender” and the darkly introspective title track testify to her emerging talents as a writer. Breezy, folk-flavored numbers like “Lifetime” and “Terrified” (the latter a duet with Jason Reeves) tap into the same uplifting grooves favored by Jason Mraz and Colbie Caillat. Even more playful, McPhee’s rendition of Melanie Safka’s “Brand New Key” is re-imagined here as a percolating shuffle. Balancing the folk touches are simmering R&B-slanted tracks like “Last Letter” and “It’s Not Right.” She delivers her finest vocal performance on the ballad “Say Goodbye,“ an exquisite expression of heartache that deserves to be her signature song. Overall a classy, emotionally resonant effort.