Fetching details from the dictionary...

alternately; in succession
不安と期待が交に胸を満たしていた。
Anxiety and expectation alternately filled my heart.
晴れと曇りが交に現れる天気だった。
The weather alternated between sunny and cloudy.
苦しみと喜びを交に味わう人生だと思う。
I think life is about experiencing suffering and joy in turn.