The crystal structures of the Hume-Rothery phases in the Cu-Zn and related alloys correlate with the average number of valence electrons per atom, or electron concentration [1]. With increasing electron concentration, the crystal structures of the alloy phases change in the sequence (see Figure 1): % MathType!MTEF!2!1!+- % feaaguart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGceaqabeaacqaHXo % qydaqadaqaaiaadAgacaWGJbGaam4yaaGaayjkaiaawMcaaiabgkzi % Ukabek7aInaabmaabaGaamOyaiaadogacaWGJbaacaGLOaGaayzkaa % GaeyOKH4Qaeq4SdC2aaeWaaeaacaWGJbGaam4Baiaad2gacaWGWbGa % amiBaiaadwgacaWG4bGaaGPaVlaadogacaWG1bGaamOyaiaadMgaca % WGJbaacaGLOaGaayzkaaGaeyOKH4QaeqyTdu2aaeWaaeaacaWGObGa % am4yaiaadchaaiaawIcacaGLPaaaaeaacaaIXaGaaiOlaiaaiodaca % aI1aGaaGzbVlabgkziUkaaywW7caaIXaGaaiOlaiaaiwdacaaMf8Ua % eyOKH4QaaGzbVlaaigdacaGGUaGaaGOnaiaaikdacaaMf8UaeyOKH4 % QaaGzbVlaaigdacaGGUaGaaG4naiaaiwdacaaMf8+aaeWaaeaacaWG % LbGaamiBaiaadwgacaWGJbGaamiDaiaadkhacaWGVbGaamOBaiaac+ % cacaWGHbGaamiDaiaad+gacaWGTbaacaGLOaGaayzkaaaaaaa!868C! $$ \begin{gathered} \alpha \left( {fcc} \right) \to \beta \left( {bcc} \right) \to \gamma \left( {complex\,cubic} \right) \to \varepsilon \left( {hcp} \right) \hfill \\ 1.35\quad \to \quad 1.5\quad \to \quad 1.62\quad \to \quad 1.75\quad \left( {electron/atom} \right) \hfill \\ \end{gathered} $$ .