Potassium, rubidium, and caesium also form sesquioxides M2O3, which may be better considered peroxide disuperoxides, .
pətˈæsiəm, ɹuːbˈɪdiəm, ænd sˈiːsiəm ˈɔːlsoʊ fˈɔːɹm sˌɛskwɪˈɑːksaɪdz ˈɛm tˈuː ˈoʊ θɹˈiː, wˌɪtʃ mˈeɪ biː bˈɛɾɚ kənsˈɪdɚd pəɹˈɑːksaɪd dɪsˌuːpɚɹˈɑːksaɪdz, .