ɪɾ ɪz ˈɔːlsoʊ nˈoʊn ðæt hˈæfniə mˈeɪ ɐdˈɑːpt tˈuː ˈʌðɚɹ ˌɔːɹθoːɹhˈɑːmbɪk mˌɛɾəstˈeɪbəl fˈeɪzᵻz spˈeɪs ɡɹˈuːp pˌiːsˌiːˈeɪ twˈɛnti wˈʌn ænd pˌiːˌɛmˈɛn twˈɛnti wˈʌn ˌoʊvɚɹ ɐ wˈaɪd ɹˈeɪndʒ ʌv pɹˈɛʃɚz ænd tˈɛmpɹɪtʃɚz, pɹɪzˈuːməbli bˌiːɪŋ ðə sˈoːɹsᵻz ʌvðə fˌɛɹoʊlɪktɹˈɪsᵻɾi əbzˈɜːvd ɪn θˈɪn fˈɪlmz ʌv hˈæfniə.
It is also known that hafnia may adopt two other orthorhombic metastable phases (space group Pca21 and Pmn21) over a wide range of pressures and temperatures, presumably being the sources of the ferroelectricity observed in thin films of hafnia.